The honest verdict on the efficiency and sustainability of air source heat pumps in the UK

by Mars
renewable energy heat source

When we committed to installing an air source heat pump (ASHP), we had reservations whether it would heat the house sufficiently. At the same time, we wanted to move away from oil so that we could be more sustainable and reduce our carbon footprint. So we took the plunge.

There are a lot of naysayers when it comes to air source heat pumps. Most say that they’re not good enough to heat homes in the UK over winter because it’s too cold and wet.

Throughout spring and autumn, our ASHP operating costs were much cheaper than oil. The real test was always going to be the winter when there was less heat in the air and where the pump has to work harder.

Luckily for our review, we had an awful December and January that was cold and damp; the worst weather conditions for ASHPs to operate in.

In the video below, we provide an honest verdict on whether we think that ASHPs are effective, efficient and sustainable in the United Kingdom.

It’s obviously worth noting that each air source heat pump is different. We have an 18kW unit from Global Energy Systems, a British manufactured pump, and results may vary from the size of your pump to the make/brand. We have not had an air source heat pump before, so we have no point of reference.

In fact, if you have an air source heat pump in the UK, I’d be very interested to hear your thoughts and feedback, and how it compares to ours, so please leave a comment below.

Consumption highs and lows of our air source heat pump

January 16, 2020, was our warmest day by average at 7.4C over the course of the winter. The coldest was January 20, 2020, at 3C. Relative humidity throughout January hovered at the 40% mark.

On January 16, 2020, we used 53.2kWh electricity (95% for central heating and 5% for hot water) to drive our air source heat pump.

By comparison, on January 20, 2020, the colder day, we used 66.6kWh (95% for central heating, and 5% for hot water).

So we used an extra 13.4kWh to heat our house when it was approximately 3.4C cooler outside. This is not insignificant from a running cost perspective over a long cold spells. The financial costs will add up. If you are going to solely use electricity to drive your central heating, that is some interesting data right there.

But that doesn’t tell the full story if you’ve got a solar PV array. The reason why it was warmer on January 16 was because it was overcast and rainy. So we produced virtually no solar (it was less than half a kilowatt hour) but the clouds didn’t allow the heat to escape.

air source heat pump ideal with weather with solar PV
January 20 was bright and fresh

January 20, however, was a lot sunnier and our solar PV produced 18kWh of electricity – we had to buy in 70kWh. On January 16, we had to buy in all our electricity as we produced close to zero, which was over 80kWh.

DateASHPSolar PVAverage Temp
Jan 16, 202052.3kWh07.4C
Jan 20, 202066.6kWh18kWh3C

It therefore appears that with solar PV assistance, cold bright days are better suited for ASHPs, because they go a long way to offsetting electricity consumption.

If you’ve got an air source heat pump without solar you’re probably better off with more gloomy, overcast warmer days and nights that trap the heat because they’ll run are efficiently. At least that’s what our data is showing us at the moment for our pump and weather conditions.

It’s just an observation at this point, but over the course of the coming year I will look into this more closely and determine whether this correlation is accurate and precise.


If you’re interested in an air source heat pump from Global Energy Systems, you can use this code when you contact them and you’ll get £200 off your installation (and we’ll get some Amazon vouchers): GESRFAF000160


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John 27 January 2021 - 09:05

I watched your video with interest.
We have just built a house with underfloor heating and an air source heat pump. We moved in pre Xmas and the system has been struggling to get the house up to our target temp of 20/21 degrees.
There are three open fires and the “building regs” incoming air vents next to the fires which have been blamed for the systems performance. We have therefore blocked the chimneys and the vents.
Annoyingly the system still struggles to get the house up to tempreture when the outside air temp goes below 2 degrees and certainly below freezing.
In reality do houses with airsource systems need a secondary heating system in very cold weather? We have been told putting log burners in the three fires places would solve the problem and give us a secondary booster heat source in extreme weather.
I would welcome your thoughts.
With thanks

Mars 27 January 2021 - 09:48

Thank you for your comments John.

Can you please let us know what size pump you have (and the brand), and how much space you’re trying to heat? Also, is it just rads or a mix of rads and underfloor heating? Do you know what the flow temperature is in your system?

In short, no, you should not require secondary booster heating with temperatures of 0-2C. We have just finished filming our next ASHP video that focuses very much on this subject. We see our house heating perfectly when it’s 5-6C outside. As soon as the temperatures start to drop below 3C, we notice a difference in the ambient temperature in some of cooler rooms, which we have put down to insulation, because the flow temperatures are still at 45C. Having said, we dropped to -5C a few days ago, and the house still remained at 21-22C, but we did consume about 85kWh on those days.

Since moving in, there have been a few milder days of 7-8C – did (or does) your house get to 20-21C and maintain these temperatures when it’s over 6C outside?

Susan+Fawn 27 January 2021 - 11:41

Hi we are now 2 months in to experiencing ASHP in our new build. (Underfloor ground and rads on first floor.) Initially we were a bit alarmed at the consumption of electricity but daily monitoring shows on milder days we use as little as 30kw with highest 69kwwhen it was minus 4 overnight. The house is being maintained at a comfortable 20/21 (it us 228 sq m). Our Grant Aerona system is 11kw.
If anything it is too warm upstairs overnight.
The aspect of the house is South at front so on sunny days front rooms naturally rise to 24 degrees in winter.

Overall our bills will be higher than normal mains gas/elec CH ystems but hopefully claiming the RHI grant will off set this for next 7yrs.

I would be interested in other ASHP users experience of annual maintenance costs/ advice of the system going forward. Do you think a maintenance contract is essential?

Edwin D Faulkner 21 March 2021 - 17:04

Hi, Interesting to see your experience . We have had a Ground source heat pump system for 10 years but the ground loop has developed a leak, the rate of which varies from top up every 3 weeks , to similar volume in 5 days. As regards performance the house has been kept at 20 C and the hot water at 48 C for the 10 years, the only issue was a 60 hour power cut due to severe snow fall wrecking the local distribution. Like you previously we had oil fired boiler which consumed >2000litres of oil and was on timer control. So we are considering changing to an air source . Your system is much larger than we are being recommended and I wondered what volume you were heating and are you like us just 2 people in the house 24/7. With the GSHP we installed cavity wall insulation and lots in the loft and it is a 7 kw system.

Mars 21 March 2021 - 21:37

Good evening Edwin. Thank you for your message and comments. I am very interested to hear more about your GSHP and it’s maintenance, and I’d be happy to answer all your questions on ASHPs. Could I just one favour please? We’re transitioning as much of our ASHP and renewable heating conversations to Renewable Heating Hub, a new dedicated site that we have just launched to discuss all matters relating to renewable heating. If it’s not too much trouble, please can you register an account here and copy your paste your comment into a new thread:

I’ll be happy to walk you through it if you have any questions.

Alistair parkin 5 May 2021 - 20:37

Sorry to hear this, it is not encouraging, for the millions of Victorian houses a and 30 and 40s houses. Seems it would involve expensive renovations. Electric boilers or even storage heaters sound a better option.

Julian M 25 November 2021 - 10:53

Electric boilers are not a sensible option for anyone, they have a CoP of just under one at all times so would cost far more to run than an air source even in cold weather, they are about 3 times as expensive as gas boilers to run.

Geoff Harvey 26 March 2021 - 21:06

We had a LG ThermaV split installed and I just could not understand why, when the temperature was way below target (say 16.5 versus 19 set) the HP was just taking it easy. When set to 19 continuously it coped with even the coldest weather but if we tried to have it at 18 during the night, it would take up to 24 hours to recover the temperature back to 19. But I think there is some strange interaction with the Honeywell wireless stat (which uses a sort of pulse modulation near to the set temperature). I eventually set up the Honeywell to pulse to 20 deg for one hour in the morning to spur it up into action after the 18 deg night time spell, and now it works fine. So what appeared to be lack of heat output turned out to a control problem that I still have not understood

bung 23 October 2021 - 06:49

Ideally you should not use a room stat at all, but instead setup weather compensation curve. i am not an expert but i think this uses the outside temperature to control your heat pump, kind of preemptively, rather than waiting for the outside weather to affect your room temp, and in tern your room stat.

Mars 1 November 2021 - 15:32

Weather compensation should be the way to set up most heat pumps, but it’s not always possible to do so in retrofits.

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Mark Rosher 22 August 2020 - 09:29

This post reminded me of the heat pump I built from an old fridge, back in 1975, for my school physics project. Powered by a vertical axis wind turbine on the roof of the science block made from a halved chemical barrel and a car alternator, it warmed the science block in winter and cooled it in summer – after a fashion.

It would help to understand how large your house is and where. Maybe that’s back in the blog somewhere (I’ve not looked, sorry). I checked and my average daily (gas) heating and electricity in January 2020 was 65kWh (4 bed detached, 4kWp solar, UK west country). I have a larger than average electricity demand (my bad).

Mars 22 August 2020 - 22:07

Thanks for dropping by Mark and leaving a comment. Your school project sounds very interesting.

We’re in the Welsh borders, and we’re heating around 4,000sqft.

Our electricity, over and above the ASHP, is a tad high and I’m fitting smart plugs to find the culprits. Your consumption seems a tad high too – do you know what’s responsible?

George Applegate 28 February 2021 - 14:38

Good news by your knowledge of this heat pump installation.

Alison Gray 2 January 2021 - 17:54

I have a Grant Aerona installed into my new build house. In the summer it’s fine, but that more to do with the fact the system doesn’t ever have to switch the underfloor heating on because the fact the house is south facing and Mother Nature heats the house for free. So it only has to heat the hot water, which, in the warmer months, it does very successfully.

In the winter on the other hand, when the temps drop to 3degrees or below, it’s absolutely appalling. It struggles to heat the house to anything over 17degrees Celsius and hot water? Forget it.

If you live somewhere that’s 20 degrees outside all year round, great. If you live in the UK, don’t install one. They’re terrible. Having spoken to 3 other residents in the estate, all 3 houses haven’t had hot water now for 3 days. Living the dream. If I could have it ripped out and have a combo boiler installed, I’d do it in a heartbeat. The site manager is going to have a lot of cold, smelly and angry people in the site office on Monday when they return after Xmas!

Mars 2 January 2021 - 21:23

Wow, sorry to hear that your ASHP has been running so poorly Alison. How hot are you able to get your hot water at this time of year? If I may ask, are your heating/electricity bills quite high?

I’m not familiar with Grant ASHPs – is there a chance they’re undersized for your property? Mind you, that wouldn’t explain its inability to heat the hot water. Getting it to 45C should not be a challenge at all.

We’ve found that 7C is the tipping point for our house and ASHP. At 2-3C we start to notice rooms getting colder. By -1C it’s more noticeable. But we’re still able to maintain most of the house at 21C.

Samantha Waby 2 January 2021 - 21:31

Hi Alison, I found your comments very interesting, if a little depressing as I’d hoped that it was just my system that was faulty, and could, therefore, be fixed.

Your problems absolutely resonate with me as the minute the temperature drops, our system becomes useless – yet incredibly expensive. We have an LG pump with underfloor heating, and, like you, I long for a gas boiler or to simply be able to walk away from our “dream”, very expensive home.

I don’t want Home Farm’s website to become anti ASHP as that’s not their aim, but if you did wish to discuss this further I’m happy for them to pass on my email so we can exchange ideas and suggestions.

You have my absolute sympathy, and I feel awareness of how ineffective these systems are needs to be highlighted whilst the gov’t throws financial incentives at them.


Mars 2 January 2021 - 21:43

We have absolutely no issue with people discussing their ASHP experiences, good or bad. We have been very pleased with our ASHP, which is not perfect by any means, but it is working pretty well.

I will forward your email address to Alison shortly.

Samantha waby 2 January 2021 - 21:54

Thank you Mars, as always that is very kind of you. I understand and appreciate that you are happy to highlight ASHPs, warts and all, but simply don’t want to hijack your passion for sustainable living, as I too, am (was) passionate about living a “greener”, gentler lifestyle. But thank you for your open attitude. Sam.

Mars 2 January 2021 - 21:59

You’re welcome Sam.

We’re very disappointed to hear your experience has been so bad in your dream house as a result of this ASHP. I’m guessing we may start to hear of more similar cases, and it would be great if we could figure out a way forward to get these kinds of issues resolved, because right now there doesn’t seem to be a body or organization that can help.

Maybe one of our followers can cast some insights.

Danny 6 March 2021 - 08:29

Hello, I have Daikin ASHP which runs my hot water and underfloor heating. End of last year I had the unit serviced and gas changed and during the last few months the heating doesn’t heat up above 19degrees during the cold periods.

Somebody mentioned to me that If the gas was not correctly removed (mode 21) the system could have to much refrigerator gas and could be the issue why the underfloor heating is not heating sufficiently.

Has anybody heard of this as possible issue?

Hot water heats fine.

Mars 6 March 2021 - 08:36

Hi Dan

The comments section on this post has grown to the point where messages and help requests have been buried. The good news is that we have built and launched a dedicated website to get these questions answered, and we would like to invite you to visit and join our new community and repost your questions there. You can do so here:

Peter 22 July 2021 - 09:15

I am just having a Samsung unit installed but have insisted on the oil boiler being left in place. I have also asked the installer to program so the hot water is on oil and the system switches from air source to oil at 5 deg outside temp. Is 5 Deg a good balance or should that be slightly higher or slightly lower. Looking for best balance between cost of heating and having enough heat to keep the house warm. Pre Airsource we run the house at 18.5 most of the time and 19.5 in the evenings with no heat from 10pm to 5:30 am

Mars 22 July 2021 - 10:10

Morning Peter. A few points:

* Heating your hot water in the winter might be more efficient, but during the late spring, summer and early autumn, you might want to consider letting your heat pump do this because there’s a lot of ambient heat around.

* The minimum temperature will be based purely on your house. Out ASHP starts to take strain at 3C when it comes to efficiency. You might want to tweak this in the winter.

* Since you’re going bivalent, you might get penalised by the RHI if your oil boiler takes on too much of the load. If you don’t have RHI, you won’t need to worry about that.

* Not knowing much about your insulation, if your heat pump has been correctly sized, you may not require your oil boiler with a target temperature of 18.5-19.C which is quite ‘cool’ – that is, however, dependant on your house.

Hope that helps.

Jill 18 November 2021 - 21:07

I have just been reading comments on ASHP’s. We have had one for the last 7 years. During the winter it has been a terrible experience. First of all it favours heating the hot water so whilst doing that the central heating goes off. By the time it returns to the central heating the temperature of the house has dropped dramatically and the pump really struggles to heat the house satisfactorily. We have underfloor heating downstairs, smart rads upstairs + solar panels. The ASHP broke down three weeks ago, the manufacturer is totally disinterested. A spare part was supplied but it did not work. We have now been 3 weeks without heating and only have hot water due to the fact we installed an immersion heater last year. We are reverting to a gas boiler next week after 7 winters of misery!

HMK 19 November 2021 - 15:29

Hi Jill, I have also had recent problems with a heat pump failure, which hopefully will be resolved next week, but I note your other problems concerning loss of heating when your heat pump goes into domestic hot water mode. This is normally due to the buffer tank installed on your heating circuit not being large enough, so there is not enough pre-heated water to maintain radiator temperature when in domestic hot water mode. Some of the heat pump units come with an integral buffer tank, this is rarely large enough for the demands of the average central heating system. My original installers guided me away from the integral buffer tank for this reason and my heat pump has happily coped with providing sufficient hot water, both domestic hot water and a central heating system with 13 standard radiators maintaining indoor temperatures up to 22C.

Mars 21 November 2021 - 21:22

What brand heat pump have you got HMK?

Mars 21 November 2021 - 21:22

That’s very disappointing to hear Jill. May I ask what the brand of the heat pump is?

Derek Marsh 15 February 2021 - 16:54

Hi Alison Gray,

I was sorry to read about your problems with your ASHP.
Mars has suggested that I try to resolve some of the readers problems. Did you get yours sorted?
If not, if you can provide details of your system Model/Type etc, along with House Type/Size, I can check the specification and see whether it is undersized for your property.

Ed 24 August 2020 - 16:57

I have used commercial heat pumps both in Michigan and in Washington State for over 30 years. I have been pleased with the energy savings and efficiency. I got likes from you for comments I made on three of Eddy Winko’s blog dating back to 2017. so I thought I would check your blog out. Warmest regards, Ed

Mars 24 August 2020 - 17:02

Hi Ed. Appreciate the comment and for taking the time to visit our site. Eddy Winko is a few years ahead of us in his country living journey, and enjoy his blog.

Michigan gets a lot colder than us in the Welsh borders. What heat pumps did you use?

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Lucy Milton 28 September 2020 - 17:26

Hello Mars,

I’ve spent a large part of today reading all your information about air source heat pumps which has been fascinating. Thank you so much for taking the time to put all this together.

I am considering using this technology for a holiday home which is based in the Lake District and rented out to guests throughout the year. We don’t’ live nearby so rely on local people to help run the cottage and sort out issues as they arise. The heating system currently uses LPG bottles and I am keen to get away from the problem of ordering and changing gas bottles. I want a system that requires as little intervention as possible!

Given that we do not live at the property, do you think the air source heat pumps are as reliable as any other heating system? I was concerned about your comments about defrosting the air pump in cold conditions. Is this done automatically or do you have to actually intervene? Can you think of anything else we should be aware of in this situation?

I’d really appreciate your thoughts

Mars 28 September 2020 - 22:21

Thanks for your comments, feedback and questions, Lucy.

In response, I can only really comment about our make of ASHP. So far, touch wood, it’s been super reliable, and the few times it did have issues, the Global Energy Team fixed the issues remotely. Their support team are available 24/7. I’m also not sure that all ASHPs have 4G connections though, and whether they are manned by support staff. This was a big consideration for us.

Don’t worry about the defrosting. This is all automated and doesn’t require manual intervention. I’d recommend that the LPG system remains so that it kicks in for a few minutes to assist with a swift defrost. This is why we left our oil boiler connected. Defrosting takes 2-3 minutes on most occasions.

Since this is a holiday home, I would automate it with as many smart thermostats and TRVs as possible, and set these to run efficiently with schedules. Guests/visitors won’t be able to change settings or heating. You will also be able to see whether everything is running as it should.

You will need a new hot cylinder for the system, and they can be quite large. That’s a notable consideration if space is tight.

I hope that helps. Let me know if you have any other questions.

Lucy Jean Milton 29 September 2020 - 10:13

Thanks Mars, got plenty to think about now.

Mars 29 September 2020 - 10:23

Great. Don’t hesitate to post any more questions if you need more clarification or assistance.

Mars 11 February 2021 - 16:41

Did you ever take the plunge and get an ASHP Lucy?

lucy 16 February 2021 - 14:24

Hi Mars,
we have deferred the project until later this year, as there is a lot of work to do in addition to the ASHP, as we want to put in new underfloor insulation and heating too.

We want to use a local firm that can do both jobs so that limits our options. We are thinking of going with a Valliant AroTHERM ASHP. One of its selling points is the refrigerant R290 with a very low Global Warming Potential (GWP) rating of 3, that allows the water to be heated up to 75 degrees C without use of mains electricity. SCOP values 3.63 for 55 degreesC and 4.8 for 35 degreesC. However the Grant UK Aerona is also a contender with SCOP 3.72 for 55 degreesC and 5.4 for 35 degreesC.

If anyone has experience of these ASHP that would be interesting to hear.

Pavan Chaudhary 16 February 2021 - 17:26

Hey Lucy. I have also opted for the Vaillant for the same reason. I am going to install it as a hybrid with a system boiler. i dont know where you are based (i am in London) but am happy to do an introduction.

Mars 16 February 2021 - 21:35

Thanks for the update Lucy. The numbers you’ve cited for the pumps are impressive.

Robbie 22 February 2021 - 09:58

I self built my house 3 years ago with ICF (insulated concrete formwork). Its 260m2 with double height vaulted ceilings. I installed a 5kw Mitsubishi Ecodan which copes sufficiently with the extreme cold we get here in Aberdeen. I have underfloor heating throughout and a 210ltr thermal store which has a huge plated heat exchanger to provide mains pressure hot water.
We have our Hive set at 23degrees and in the recent cold snap of -8degrees it coped sufficiently.
A few people on here seem to be missing the point. It’s not the heat pump that’s the problem. It’s how well insulated and airtight your house is!
Heat loss is everything when using an ashp. Also flow rate is critical for the performance of the pump to live up to manufacturers instructions.
It always amuses me when people slate their equipment when it’s highly unlikely it was sized for purpose.
I’m a heat pump installer and there’s a phenomenal amount of information required in a heat loss calculation before a correctly sized heat pump should be installed.
An average new build has 5 air changes per hour. Mine has 1.5. This all down to how well insulated and airtight the building is.
If you get this right from the start then it doesn’t matter which heat pump you opt for, it’ll work perfectly!
BTW Vaillant aroTherm plus is what I’d recommend.

Mars 22 February 2021 - 10:22

Thank you for your professional comments and insights, which are greatly appreciated. ASHPs do work. That is not in question, and we completely agree that insulation is extremely important and cannot be understated. The one that we’ve now discovered, and that so many other consumers have too, is that the ASHP systems (especially in retrofits) have not been designed and installed correctly, and as a result hot water is not getting where it should leading accelerated heat-loss which the pump cannot satisfy. This appears to be the case for us and that’s something we’re hopefully going to get sorted out next week. Thanks again for your comments Robbie.

Graeme 24 March 2021 - 16:13

One question , can you have a hot shower/bath with ashp? Eon are installing one at my home in next few weeks. Cheers

Mars 24 March 2021 - 17:35

Yes, of course you can. The ASHP will get temperature to 50C with a relative amount of efficiency. Our pump also prioritises hot water over central heating.

On a related note since you’re joining the world of ai red source heat pumps we would like to invite you to join Renewable Heating Hub where you can participate in our forum discussions and get answers to questions about renewable heating and heat pumps

Steve Brockie 3 August 2021 - 20:53

Hi Robbie & everyone commenting.
I also live in Aberdeen, we are considering retrofitting an ASHP to the house we bought in Nov currently heated by LPG.
Robbie you mentioned it all depends on your insulation and heat moss, currently our house struggles on cold days to get to 20 degrees and when the heating goes off it plummets down through the night to about 14.
The house is 30 years old, cavity walls, 50mm underfloor insulation and will soon have 300mm loft insulation. It’s 176sqm 1.5 storey and we’ve been recommend to fit a 17hz pump. Would you say that if you have a lot of heat loss, a bigger pump will help to achieve and maintain the desired temp?

Mars 4 August 2021 - 07:33

Thanks for your comments Steve. Due to the structure of comments on our blog, where replies get lost, we created a new website that facilitates better conversations on renewable heating.

We would like to invite you to join Renewable Heating Hub where you can participate in our forum discussions and get answers to questions about renewable heating and heat pumps

Simply register there and copy and paste your questions into a new forum discussion. You’ll get a lot more advice and feedback. Let me know if you have any questions.

Tony Ambler 4 October 2020 - 12:45

We took the plunge and purchased an ASHP for our house in the UK and decided on the Mitsubishi Ecodan. We also purchased 14 solar panels and storage batteries that will store 4.8 kW of power. We did this because we had to renew our 24 year old oil boiler which was well past it’s best by date. We used around £600 of electricity and 2200 liters of oil per year (approx) which cost us, last year (2019) around £1100. Total energy cost £1700. Throughout the summer our electricity cost has been reduced by about 40% and, of course, our oil bill had been removed. The colder months have seen an increase in our electricity consumption especially when we generate very little through the panels. We found that our panels through out the summer powered all of our white goods, lighting and TV’s etc and charged our batteries but heavy consumption units like our range cooker needed the grid. The winter is looking like it will use significantly more electricity but I am reasonably hopeful that it will be far less than the old combined oil and electricity cost. I will let you know.

Mars 4 October 2020 - 12:54

Thank you for taking the time to share your ASHP numbers. These are very insightful and should be helpful to users looking at an Ecodan solution. What size is your Ecodan ASHP, and to help us get an additional insight, what is is your approximate floorspace that you’re heating in your property?

The ASHP does draw a lot more power over winter (in our experience), but we find that it’s still far more effective than oil.

Out of curiosity, will you be running your ASHP heating 24/7 over the winter and have you automated your central heating in any way?

Thank you once again for sharing your data.

Sam Waby 28 December 2020 - 07:26

The noise from our LG heat pump at night (& during the day at times) means I haven’t slept properly since we bought our new eco-house. I have had the system checked and apparently there is no problem. I note that yours is situated away from the main house. Is this a problem at all as my installer insists it should not be done and decreases efficiency? Short of selling up, it may be our only option. What’s your opinion please? We have spoken before, and the situation has not improved unfortunately.

Mars 28 December 2020 - 10:21

Sorry to hear that you’re still having issues Sam. I find it remarkable that your system has been given the all clear, given that it clearly doesn’t work and isn’t working the way it should. Also, your neighbour’s system is working so there’s direct point of comparison, which I find astonishing.

The all clear – was it given by the installers or did LG also send out a representative. At this stage, I think the best thing to do is exert as much public pressure on LG as possible – more on that later.

Moving the pump is an option from a noise perspective, but that won’t resolve the fact that it’s not working as it should – if I recall it’s using loads of power and not heating very well. From an efficiency perspective, setting the pump away might have a small impact, but the heat-loss pipe we used is very good and we have no issues maintaining our flow rate at 45C. To be clear, we moved our pump for aesthetic reasons. If we’d positioned it next to the house, there is no chance we’d hear it inside our kitchen or master bedroom (which would have been the two closest rooms). This is a clear indication that your pump is not working as it should and this should not drive you out of your dream home.

I would pursue the LG angle and make it their problem. The ASHP market in the UK is heating up and manufactures will be fighting for market share, so negative comments and feedback in the public domain will hurt them since they’re all fighting to wrestle away business from Mitsubishi. From my limited insights and knowledge, LG do make excellent heat pumps, so the fact that yours is very noisy and not working indicates an issue with the pump. I would contact their tech support and also see if you can find senior management that you can email.

Do you know if the pump is still under warranty?

Can you please record your ASHP and send us a short video so that we can hear the noise? You can send it to us using something to

Derek Marsh 15 February 2021 - 17:23

Hi Samantha Waby,

I was sorry to read about your problems with your ASHP.
Mars has suggested that I try to resolve some of the readers problems. Did you get yours sorted?
A noisy ASHP is normally a sign that there is something wrong. It could be as simple as too much or too little Refrigerant Gas, or something more serious.

Sam 16 February 2021 - 08:33

Morning Derek,
Thanks for your message, it’s very kind of you to try to help people with issues.

Our Therma V pump is brand new, and during milder spells like this works with a low hum and whoosh, which is ok. However, when it’s cold (below about 3° probably) it emits a constant buzzing noise which can be heard above our TV and is too loud to be able to sleep in our bedroom – moving us into a spare.

The builder located it rather thoughtlessly on a wall in a narrow courtyard part of our garden and it faces onto a fence and I wonder if that could be the problem?

We are considering having it moved (is this possible), buying a surround, which the manufacturer claims will reduce sound by 20 decibels, or replacing it with a Mitsubishi, as the LG engineer who came and checked told us they were quieter. This final solution may sound drastic but given that over Christmas we were considering selling this house that we only purchased in September shows just how much this noise is impacting on our lives. It feels like living with tinnitus for the cold months.

Any thoughts or recommendations would be so appreciated.

Thank you, Sam.

Derek Marsh 17 February 2021 - 00:55

Hi Sam,

I have only just seen your message, otherwise I would have replied earlier. You don’t have to thank me, I am happy to be able to help others whilst we all suffer lockdown. Besides you have a big plus in your favour, my Daughter’s name is Samantha.
Reading your most recent comments I suspect that your ASHP is badly sited, not only from the noise aspect but also from an efficiency point of view. It may also not be functioning correctly, but we will explore that later.
Looking at the Technical Specification for LG Therma V (though it would be useful if you could tell me which model you have) it states a noise level of 52dB(A), which is slighly higher than that quoted for an Ecodan, but within the normally acceptable range.

Rather than send loads of e-mails back and forth, since it is rather difficult fault finding via e-mail (though not impossible), I would suggest that you initially watch the following video.
MESH Energy webinar technology masterclass: Air source heat pumps.
I found it whilst I was researching ASHP with a view to getting one myself. I have no involvement with the company, so there is no conflict of interest. I would just say that the video explains in sufficient detail how ASHP should be installed and commissioned for best operation,
Watch the video and then come back to me with any questions you have on the best way to get you a good night’s sleep, without you having to wait until you are old and can just remove your hearing aid.

Haresh Patel 5 October 2020 - 11:53

I wonder if anyone has done a comparative study between air source heat pump and ground source pump. Would be very grateful if you can kindly share your experience.

I am planning to install ground source heat pump for my London (UK) home following refurbishment.

Mars 5 October 2020 - 15:19

Thank you for your comment and questions Haresh. We looked at ground source as a potential solution for our heating, but didn’t pursue it because the installation was going to be very invasive and the costs were prohibitive. So we went down the route of an ASHP which was cheaper and much simpler to install.

As a result, I don’t have any comparative data, but I do know that GSHPs are more efficient than ASHPs. If you have the land and the funds, it will probably be the better option, and the RHI repayments are also much higher.

Andrew Scott 18 November 2020 - 13:20

We built a new house in Cornwall in 2016. We are fortunate in that a small stream runs through our property, so we opted for a GSHP and a plate heat exchanger which is quite small and much cheaper than either horizontal or vertical ground arrays. The GSHP is rated at 6.5 kW, and we have a 3.5 kW solar PV system. The house is a modest 3 bed detached and with just the two of us in residence we are not thrashing our appliances. Being a new build I have no comparative data, but our annual consumption is 3916 kWh with a max monthly in January of 590 kWh and min monthly in July of 156 kWh. Generation is 3444 kWh annually with a max monthly of 484 kWh in July and monthly min of 76 kWh in January. These figures are for 2019, but very similar from 2017 to 2020. The upshot of this is that our electricity bills are around £700 pa and FIT payments approx £550, so our annual costs are £150. On top of that we are claiming our RHI payments which are approx. £1200 pa. This is paid for 7 years so we will recover approx £7k which is the material cost of the GSHP and associated parts. This was all supplied by Kensa heat pumps. Hope this is useful information.

Mars 19 November 2020 - 21:30

That’s great Andrew. Thank you sharing. Some very interesting numbers and great as a comparison.

Jane sndrews 19 October 2021 - 10:56

Hi not happy with air source heating. Every winter there is a problem. It cost us about 10 pound per day in winter. We find it expensive, not like they advertise. If I had a choice I would change but that would cost a lot. Sorry no pound sign on phone. Jane 🤔💷

Mars 19 October 2021 - 10:59

That’s interesting Jane. We also found the running costs last winter very high, and it’s going to be even more expensive this winter with the astronomical electricity tariffs.

p harvey 8 October 2020 - 20:00

They are noisy and take too much space. unless you are replacing with oil and live in the country in a detached property – you cannot beat GAS

Mars 11 October 2020 - 09:44

When it comes to central heating, mains gas is the most efficient way to heat a property. But it’s not the cleanest and does have a CO2 impact. I’ve read that many ASHP manufacturers are working on smaller form factor, quieter, more efficient models for urban settings, and the UK government is working on getting ASHPs integrated into new builds instead of gas boilers.

Brian Mallalieu 30 October 2020 - 12:52

Thanks for your informative & interesting video. I take it the ASHP is also providing you with DHWS for washing etc. and it would be helpful if you provided more details about your experience with it and comparisons & costs hitherto?

Mars 30 October 2020 - 21:09

Thank you Brian. We’ve actually just finished recording a new video that covers many of the questions you’ve raised. I will reply here when the new video is ready and will share a link.

Danielle Strachan 30 October 2020 - 19:26

This has been very interesting to read thank you- we are currently looking into getting an outdoor heat pump.

We have just been told the total cost is £11k but after w government grant we only need to pay 3.5k- but I’ll still not sure if it’ll be better for us than what we have. We live in w small town in Scotland and our town doesn’t have gas at all.
We have an old economy 7 electric boiler.

I’m gonna do a bit more research before we make a decision

Mars 30 October 2020 - 21:19

Thanks for the feedback Danielle. You may want to look into this, as I’m not sure it’s 100% accurate, but once you get the government grant, you’ll still be eligible for the RHI scheme so you can get even more money back. Definitely worth checking it out.

David 11 November 2020 - 17:14

The green energy grant and rhi payments would come from the same pot of money allocated to your project, so the total amount would be the same. If you use the grant that amount would get subtracted from the total rhi you would otherwise receive. Benefit is a big lump near the start as opposed to bring spread over 7 years. We have 1 property on an ashp installed 2 years ago and it’s amazing…. Rented out currently. Our own house is having 1 fitted in a few weeks, a gen 6 Samsung 16kw monobloc. The other house is a gen 5 in a big 3 bed semi, average Elec cost is 80 quid per month

Mars 11 November 2020 - 21:18

Thanks for the clarification David, and for answering this. We would have preferred the lump sum to be honest.

£80/month is excellent on the three bed semi.

Danielle Strachan 4 May 2021 - 22:10

After all this time through Covid we finally got an ecodan heat pump installed after 3 cancellations due to Covid. It’s only day one so in early stages. But the radiators don’t seem to want to go last 16 degrees even though it’s set at 22 😂

Richard Dobbs 17 November 2020 - 10:54

Very interested in your helpful blog Mars. We are looking to install ASHP. We are a flat and can install on the balcony. We are around 150m2 area overall and have 2.7m high ceilings. Any thought on output needed? We are ‘all electric’ 3 phase with a wet rad system so currently two 9 kW boilers really use a lot of juice! 7 kWh LG R32 is recommended but sounded a bit underpowered to me….

Mars 19 November 2020 - 21:35

Thanks for the comment and feedback Richard. I can’t make a call on the sizing and whether it’d be underpowered, but a 7kW may be on the small side. I’d recommend, Covid-permitting, to get another 1-2 installers to quote and see what size they’d recommend.

Wolfgang Küchler 20 November 2020 - 15:50

No one has mentioned insulation? Can you – and other commenters – tell us anything about how well insulated your homes are, the type of windows, draught stopping? There’s a lot of concern about putting heat pumps into thermally “leaky” buildings. Also ground source is supposed to be better, also in terms of noise – any comments on that from anyone?

Andrew Scott 20 November 2020 - 18:23

We built a new property so were able to design a well insulated thermally efficient house. We have 100mm foil backed PU insulation layer in the floor with underfloor heating in a 60mm screed on top, the internal structure is timber frame with 125mm foil backed PU insulation in the walls and roof. We have high efficiency double glazed windows and doors. We have a Kensa ground source heat pump, which is quite noisy, but no more than the oil fired boiler at our previous house and as we designed the house we created a separate small room to house the boiler UFH pumps, manifolds and all electrical and IT equipment. Being in a separate room, the noise is no more than that from our fridge/freezer in the kitchen

Mars 22 November 2020 - 08:40

We spend a lot of time insulating our period property. We have double glazed windows and foil backed insulation in our walls, and whenever we come across a draft, we address this to prevent heat loss. Our property is by no means perfect when it comes to being insulated, but the ASHP still manages quite well. The better we insulate, the more we’ll increase our efficiency.

RALPH Brunjes 21 November 2020 - 00:21

Before we had our heat pump installed we happy and the anual bill for gas was about £2000-£3000 , since getting rid of LPG and haveing all the house run on electric our electric bill is £1320 we also run two big American washer and drier. We do have solar panels and get money back each reading but obviously depending on weather it is different each time . We also live in the far North of Scotland , wet windy cold hot. Three seasons in one day.
So far we have been very happy with the heating unit apart from the control panel, it goes crazy every time we have a power cut . But we were told that it is an old model.
With us both being disabled we tend to have the heating on 24/7.
So in conclusion I personally think that it is a great unit . We have a double fan unit and it heats a large 4 bedroom 2 reception detached bungalow.

Mars 21 November 2020 - 08:51

That’s brilliant Ralph. Thanks for sharing, and it’s great to hear that your ASHP is getting the job done in the north of Scotland.

steven murphy 26 November 2020 - 15:57

they are noisy – unsightly – and expensive – neighbours complained about fan noise and heat exchanger fan
GAS IS THE BEST IF YOU ARE ON THE GRID – had to have additional heating on in the water and electric boost for the hot water
could not wait to get rid of it
never again

Mars 28 November 2020 - 17:41

Sorry to hear about your ASHP experience. Can I ask what pump you had?

Ian Knight 29 November 2020 - 11:44

Hello. I’m thinking of replacing our conventional gas boiler (CH & HW) with one, or two, air source heat pump(s). i.e either one to do both jobs or one to do the CH and a smaller independent (internal?) one for the HW. We have a 5-bed detached house with hot water tank and radiators. Double glazing and insulation are OK but may need improving. We’re on mains gas but obviously that’s a limited resource and prices are only going to increase, our boiler will need replacing soon so I’m thinking ahead about a renewable alternative.

A couple of initial queries you may be able to help with:
– the size (power) of unit required. Our gas boiler is rated at 18kW but some websites indicate a 4 bed house needs just an 8kW unit.
– whether the heat pump can be a straight swap for our boiler, or whether a new cylinder is also needed. Some manufacturers imply that the cylinder must be replaced, but in other places they say it can be a straight swap. Your write-up seems not to mention the cylinder.
– running noise. The main components are a big fan and a compressor. Although we are in an urban neighbourhood we want to keep the noise levels down. Your house seems fairly rural, do you have a sound recording of the unit runnung?

Thanks, Ian.

Mars 29 November 2020 - 22:10

Thank you for the comments and questions Ian.

Pertaining to the noise, I don’t think it’s as invasive as people make out, but it’ll vary from pump to pump. Each situation and placement will also impact the sound. At around the 16:00 of this video you’ll get an idea of the fan noise:

As far as the cylinder is concerned, yes, you’ll need a new one. We speak about our full installation experience here, and discuss the new hot water cylinder:

I hope that helps.

Desiree White 8 December 2020 - 21:16

Have recently had a ashy installed to replace an old gas boiler. Although it heats the house up well am worried about the running costs. Listening to your video would it be better to keep the temperature constant all day. Have a Nest thermostat and use this to control the temperature. At moment I have the heating set to 15.5 at night and 18 during the day but wonder if it would be better set at constant 18.

Mars 8 December 2020 - 21:44

Thank you for your feedback Desiree.

We’re now in our second winter, and heating costs are always a consideration. Your 2.5C gap between economy and comfort temperatures is quite large. We’ve noticed that bridging 2.5-3C takes a long time and draws a lot of energy.

For us, it’s been a lot of trial and error. Run your system the way you have for two days and note how much electricity you’ve used to drive your heating. Then adjust to 18C 24/7 for two days and note down the electricity usage. Then compare. Also, if possible, make a note of outdoor ambient temperatures as they may skew figures. At the moment it’s consistently cold, so could be a good time to experiment. Your heat pump, like ours, may give you all this data.

Then see what’s best for you, and your house.

Please us know what the outcome is.

Yvonne Warman 23 December 2020 - 14:17

We live in a detached house of about 100sq Mtrs. Correctly our newish economy 7 storage radiators plus hot water costs about £1600 a year. Would an ashp save me money?

Mars 26 December 2020 - 13:57

Thanks for the question. Do you have a wet central heating system in place? ASHPs will probably be more efficient than storage radiators.

Rosie 1 January 2021 - 21:48

Hi, we currently have a gas warm air central heating system in our 5 bed house and given we are considering replacing the majority of the floor downstairs and likely with underfloor heating, we want to look at ashp. Possibly alongside pv solar panels. Current heating just has a dual which has to be turned to alter heat levels which means it’s hard to control temperature. Is ashp likely to save us money? As well as green incentive.
We are detached but very close to neighbours, is the noise likely to cause us all issues?

Mars 1 January 2021 - 22:02

Thanks for the comment Rosie.

ASHPs will not outperform mains gas systems, but they are greener and better for the environment.

The green incentive payments are very helpful but will not cover the full cost of most ASHP installations. We get RHI payments and they are very helpful.

Would definitely recommend solar PV, if you have a favorable site for them.

Noise will vary from pump to pump. We don’t find ours that noisy, but there are some models that are quite noticeable and annoying. Most pumps publish their noise levels, so it’s worth studying those.

Hope that answers your questions.

Rosie 2 January 2021 - 01:33

Thank you, that’s what I’ve been reading. We plan to be in the house at least 30 years, so whilst we are replacing the floor, feel like we should consider underfloor heating and therefore ashp, especially considering the future of gas. But don’t want to do this at increased ongoing financial cost.
How would we estimate the potential annual cost?

Samantha Waby 2 January 2021 - 09:49

Hi Rosie,
Apologies to Home Farm who I know are great supporters of heat pumps;however, I would personally ask you to think extremely carefully before proceeding.

We purchased a £700,000 eco house in September which has underfloor heating powered by a pump. 3 months later we will we could sell up and walk away. The noise from the pump is horrendous and can be heard over the tv, and I haven’t been able to sleep without earplugs or tablets – and even then am disturbed by the noise.

The house is never warm. We have given up on heating 4 bedrooms and struggle to get others above 17 degrees.

And all this for bills of nearly £300/ month. I accept this is simply our experience, but as I dearly wish I’d never bought a property with this technology, I wish someone had shared these possible issues with me.

Good luck,

Mars 2 January 2021 - 10:15

Sam raises valid concerns about ASHPs. If they’ve not been correctly installed and commissioned they can run very poorly and inefficiently, as appears to the case in Sam’s eco property. We had a slight issue with our ASHP just before the new year (we’ll post a video about this in a week’s time) and it can become stressful because heating in the UK is so important over the winter. Having said that, this would apply to any other form of heating too, where the oil boiler we inherited was also not commissioned or set up properly.

From our experience, when committing to an ASHP there are two major factors that have to be considered:

1. The brand and size of the ASHP matter.
2. Selecting a competent, professional installer.

When we were getting quotes for ASHPs, half of the installers that came across were cowboys and didn’t instil us with any sense of confidence. Many were central heating installers that decided that there was money to be made installing ASHPs. After months of deliberation and weighing things up, we opted for Global Energy Systems’ ASHP (the 18kW model) and went with the installers they recommended, which they had vetted on our behalf: All Seasons.

The GES pump is excellent (but does require monitoring and tweaking from time to time, as will the case with most retrofit projects) but the All Seasons installation team were professional and competent, and who had experience installing ASHPs. For us, it all hinges on the installation team (which was also the case with our solar PV system we installed), because you can have the best equipment in the world, but if it’s installed incorrectly or not set up for a property’s requirements, it won’t work as it should, which is sadly what I think is the issue with Sam’s ASHP.

Mars 2 January 2021 - 09:57

Morning Rosie.

We’ve just shared our December monthly costs in this post:

This is the heaviest month we’ve had in terms of running costs, because of the cold, wet, humid weather. I hope that helps.

Rosie 1 February 2021 - 22:07

Thanks. Other than the unit, what physical alterations are needed to heat a property by ashp?
I am assuming underfloor heating is a wet system so would be costly to dig up the floor to install?
We have a warm air heating unit but no ducting. And the ashp would probably need to be on the rear of the property and I’m worried the front of the house would be cold?

Mars 1 February 2021 - 22:14

I’m not au fait with warm air systems, but ASHPs should be able drive a radiator only central heating system. Our upstairs rooms are rads only, and we maintain them at 21C.

While UFH works well with ASHPs, the right size pump with rads is also effective.

Brian Mallalieu 8 February 2021 - 15:57

Rosie, do you have good all round insulation to the rooms being considered for u/floor heating? If so, have you considered DIY elecric heating e.g. Warmup?

Sue Fawn 4 January 2021 - 22:57

New user of ASHP

Mars 5 January 2021 - 08:23

Congratulations Sue. What ASHP did you install and what has your experience been like so far?

Susan Fawn 5 January 2021 - 11:06

It was installed by our developer in 4 new homes on Welsh border. A Grant system.

Mars 6 January 2021 - 08:53

How long have you been running the system and is it keeping you warm this winter?

Susan Fawn 6 January 2021 - 09:05

Hi Mars
Only about 5 weeks since we moved in. We have sophisticated digital room sensors in each ground floor room underfloor heating and rads on first floor. There are week and weekend settings and one on first floor setting the temp for all bedrooms. Most are set at 20.5 with bedrooms at 19, nd the house remains warm 24/7.
We have used 1100 kws in about 30 days incl appliances etc.
I will be applying for the Renewable energy incentive scheme.

Will be interesting to see the net cost over 12 months. We have moved from the sunny south coast with south facing gardens to a wetter climate and rural setting but well worth it for the peace/hills around us and views to die for!


Mars 6 January 2021 - 10:05

Sounds like you’ve got a good setup that’s working well, and it also sounds like you’ve moved to a beautiful part of the world. Great to hear.

Definitely apply for the RHI because the repayments are very good. Please keep us posted on the performance and effectiveness of your ASHP.

Dv 6 January 2021 - 20:20

Been looking at ASHP for our cottage and very pleased I found this site, while not decided on a brand I’ve found installers have their favourites, I would be keen to hear of noise levels for Nibe and Valiant if anyone’s got experience of them

Mars 7 January 2021 - 09:59

Thanks for the comments and feedback David. It’ll be interesting to hear if anyone has used Nibe or Valiant. You should also give Global Energy Systems a ring (the manufacturer’s of our pump) because they have some very good pumps and their customer service and support has been excellent.

TD 8 January 2021 - 10:17

Thanks for putting the video together Mars. Very informative and interesting.

We also live in a converted farmhouse (Yorkshire) and have no mains gas, so our primary heat source for central heating and hot water is oil. The boiler is now close to 30 years old and I am sure it won’t be long before it fails beyond economic repair. We only rum the boiler through the winter and only in the evenings. It’s a five bedroomed property with around 240sq M floorspace. We only have radiators, so no underfloor heating. Through the summer and in the winter we also run an immersion heater on Economy 7 to provide, or boost the hot water.

I am in discussion with an ASHP installer about converting our system, including upgrading the radiators and installing a new heat store tank.

Would you mind telling me roughly what your floorspace is and what was the output of your old oil boiler that the 16kW ASHP replaced. How many rooms are there in your farmhouse?

We like the idea of 24/7 background heat and if we went with a well set up ASHP we would be able to eliminate the estimated £500 per annum immersion heater cost , as well as the 2400 litres of oil we use.

Do you know how many kW your ASHP has used over the period of a full year.

It would be great if I could get an idea of how your property compares to ours and how much electricity you have used to drive the ASHP. Whilst I understand the theory and the sales pitch being given to me by the installer, it would make sense to sense check their projections against a similar property. They are proposing a 17kW unit.

Thanks in advance for any insight.

Mars 8 January 2021 - 16:53

Thanks for the feedback, comments and questions TD.

We’re heating around 4,000 sqft (370sqm), which consists of our large downstairs living area, entrance hallway, five beds, TV room and annex.

I’ve just posted our 2020 ASHP consumption which will give you a good idea of running costs:

The key to saving is to get the lowest possible electricity tariff: as close to 10p/kWh.

A 17kW sounds like a good size for your property because our 18kW handles our requirements. May I ask what brand up your installer is proposing?

What’s your general insulation like, because that’ll dictate your pump’s efficiency.

TD 8 January 2021 - 17:48

Thanks for the quick reply Mars.
Unfortunately the installers have come back to me this afternoon and told me that it doesn’t look cost effective. Mainly due to the location, layout and age of the property.
Their calculations indicate that we would need 2 x 12kW ASHP units to guarantee sufficient output. And we would need a 3 phase electricity supply to handle the start up surge current requirements of both units (even though the units are DC inverter based). They were proposing units manufactured by Grant.
They did suggest that a hybrid type system could be an option, utilising a smaller oil boiler to supplement the ASHP, but they recognised that again this wasn’t a cost effective solution, due to the initial capital cost.

I may get a second opinion. But as they were so thorough in their evaluation and honest enough to advise against it, I am not sure that a second opinion will tell me a great deal more.

I’m going to update the boiler controls so we can trial running the boiler for longer periods, but with a lower room temperature setting overnight. Doing this should eliminate the need for the immersion heater. Also, I will balance all the radiator flows and adjust the circulation pump speed so I can optimise the delta between the flow and return temperatures.

Then I’ll start investigating more efficient oil boilers, as sooner or later our old one is going to pack up completely and be too expensive to repair.

Never a dull moment!!
Thanks again for your reply

Mars 8 January 2021 - 21:29

Thanks for the update TD. From what you’ve said, it seems they are a credible company and aren’t trying to push the sale. That’s heartening.

On the back of that comment, I’d definitely recommend a second opinion. We did have one company proper to us we needed two Ecodans, which wasn’t the case at all.

I’d recommend All Seasons, who are based in Sheffield, and they’re the guys that installed our system. I think they cover all brands of ASHPs, but focus on Mitsubishi. They were a professional, experienced outfit:

Running the boiler for longer at lower temperatures seems like a good idea.

As for balancing, we’re still having horrible issues with two rooms (one of which is the TV room) which I need to get on top of. Just not enough hot water getting through.

Like you said, there’s never a dull moment with central heating system.

TD 2 February 2021 - 16:15

Second installer has looked at the house and they have also concluded that we would need 26KW ASHP and most of the radiators changing for it to work satisfactorily.

So now working on plan B which is a more efficient condensing oil boiler which we will locate externally to reduce noise and free up space in the kitchen. Awaiting two quotations. Part of the work will involve converting the hot water and central heating circuits to valved control which I am told helps efficiency as well. I have also installed a Hive control system myself which is giving us better control over the times and temperatures for the central heating.

Since we are now running the boiler more often I have been able to switch off the electrical immersion heater which ran on Economy 7 overnight with a 2 hour boost around tea time.
We don’t have a smart meter, but I have been monitoring the E7 consumption for close to a month now and it has dropped by an average 4.5KwH per night over the past 30 days. I’m not sure exactly how much we have saved by not running the immersion heater through the day, but we have also not needed to put on any electric heaters during the day. Looking at the average daily consumption from historic bills for winter last year, compared to the last 30 days, I think we are saving around 4.6KwH on the day rate as well. On our current tariff from E.ON the combined day and night savings equate to circa £335 a year.

It’s early days and I don’t yet know how much extra oil we are putting through the old boiler, but the £335 electricity saving will buy us close to 850 litres of oil to offset against the extra boiler use.

Hoping that a new condensing boiler with a claimed efficiency of +/- 94% and a more efficient valved flow control system will help to reduce our oil consumption significantly compared to the old boiler which has a published efficiency of 70%. (and that assumes it is running as well as possible!!)

At 94% efficiency I think it should also be more economical to heat the hot water only through the summer than using Economy 7. If I’ve got my maths correct. then our current Eco7 cost per unit is £0.066 (and likely to increase when the current contract expires in April). 1 litre of kerosene is £0.35 which works out at around £0.037 per unit at a 94% efficiency.

I guess time will tell !!

Nigel 27 March 2021 - 23:25

TD, I’m looking for a reputable ASHP Installer in Yorkshire, would you mind saying which companies advised you on your system?

Susan Fawn 9 January 2021 - 11:30

I have been reading your comments about lowest tariffs for electricity. We can’t seem to find anything much under 17p per kw. and 20p per day standing charge.Even getting a supplier to respond in offering a contract is proving difficult in this climate. We have been in our new build home since 30 Nov and still waiting for a welcome pack.

Mars 9 January 2021 - 11:40

For the past few years we’ve managed to get rates around 14p/kWh, with standing days rates that were over 20p. This is the first year we stalled and couldn’t find anything less than 16p/kWh (that was with GOTO Energy), until George suggested Symbio to us which was just under 11p/kWh with a standing rate of 20p. Every year, when I look for new suppliers, I’m astonished at how many providers (large and small) have tariffs around or over 25p/kWh. Crazy.

And as you’ve pointed out, the current Covid situation is just going to make it more challenging.

Iain 13 February 2021 - 22:00

My wife recommends Flipper whom she has used for years for a house she managed. For a small annual fee they will monitor electricity prices and will suggest that you switch to keep in the best available deal. They ask you if you would like to switch then do it for you if you say yes. She swears by them.

Mars 14 February 2021 - 07:54

Thank you Iain. I’m going to check them out right now.

Mars 14 February 2021 - 22:54

Signed up with them today. Let’s see if they can find a cheaper provider.

Julian C 8 January 2021 - 17:45

Very useful site – thank you. We live in a 2700sqft 20 year old bungalow. We have triple glazed, doubled the loft insulation to 300mm, blocked up drafts, a new A Rated oil boiler 6 years ago, 4kW of Solar PV and an electric diverter that uses spare electric to heat hot water. An electric car too 🙂 We currently use about 1200-1500L of oil per year and about £45 of electric / month. Our home has an EPC rating of B and energy demand of 20,000kWh.
I continue to be keen to drive down our CO2 output, so was investigating an ASHP solution. Mrs C has said “NO” to underfloor heating or radiator enlargement (note: we already have quite a lot and large radiators).
I have been investigating an Hybrid ASHP system – an 8kW Samsung unit would be added to our existing oil boiler to cover “80%” of our heating needs, the remaining 20% the oil boiler would kick in. It would be funded through RHI – they system would be cost neutral, only having to pay for electricity.
So my questions would be: your thoughts on an Hybrid System? I note you kept your old boiler – how often does it kick in? Where did you find an energy supplier at 10p/kWh? I pay 14.5p and 5p for 4hrs at night to charge the EV. Any advice or wisdom gratefully received

Mars 8 January 2021 - 18:09

Thanks for the comment and questions Julian. Your house and set up sound great. Love the drive towards lower CO2 footprint.

On the subject of UFH and larger rads, those are requirements for houses that lack insulation and that lose a lot of heat. That’ll be something an installer can evaluate at a site visit.

I have some “issues” with bivalent systems. Ours included. The ASHP will run 99.9% of the time and get small boosts from the oil boiler, as is the case for us. The issues occur when we need to switch over fully to our oil boiler. I’ll be tackling that in our next video. Not sure how you’d get an 80/20 split, and what implications that has for RHI repayments, because the RHI want a higher percentage of ASHP usage.

As an initial thought, the 8kW Samsung might be a tad small for your footprint, but that’ll be something that’s addressed at your site visit as it sounds like your insulation is excellent. It’ll be interesting to see what your heat loss calculations come back at.

Our boiler kicks in on most days for a total of 1-2 minutes. Minimal.

Energy at 10p/kWh: George, who posts and comments on our site, recommended Symbio Energy who have recently switched to. Our previous rates were 15-16.5p. So far Symbio have been great.

I’d definitely get an installer or two out and see what they say. Would be happy to share my thoughts on their proposals.

Julian C 1 February 2021 - 23:24

Evening Mars. Thanks for the continued ASHP discussion on this site. I think I’m moving away from the idea of an hybrid system, keeping our oil boiler & adding an 8kW ASHP. Instead I’m pursuing the idea of a Daikin Altherma 3H HT 16kW system. HT = high temperature. It’s also super quiet. Calcs show an electric demand of 7300kWh to deliver the 20000kW of heat. Daikin has a 10 year fixed price service package which I like. But their monitoring and links to agile tariffs is missing. I’m also looking at the mixergy hot water tank.

LJA 19 January 2021 - 10:53

Hi Mars,
Thank you for sharing your data and experiences, all very interesting. Currently planning a new build in the North of Scotland and hoping to install a 7kW Panasonic ASHP. House is a single storey, 110m2 with wet under floor heating throughout. The ASHP must also provide hot water (2 sinks and a shower) for 2 adults, and a heated towel rail in the bathroom. We have had guidance on selecting the heat pump and tanks, and we are happy with the size. The house will be very well insulated with triple glazing, although not quite passivhaus standard. We were advised around 3kW to heat the home. We therefore hope that the ASHP will rarely need to be running at 7kW, and mostly be using much less power.
I just wanted to ask, from your experience, how does the ASHP usage vary over the day – how often does your system draw the full 18.8kW?

Mars 19 January 2021 - 11:04

Thank you for your comments and feedback LJA. It sounds like your new house in Scotland will be well insulated and the ASHP should work well.

In response to your question, there’s something very misleading about the ‘sizing’ names for ASHPs. I recently asked an ASHP engineer about this, and he had no answer for me. He couldn’t answer my question as to why our ASHP is 18kW in name. To clarify this point further, the 18kW system we have, never draws 18kW of power – doesn’t even come close. Our system, at peak, draws between 3-4kWh of electricity, which is why on very cold and wet days (with frequent defrost sessions) we consume about 80kWh of electricity over 24 hours (about 3.5kW per hour).

Your heat pump, despite the figure that’s been quoted in the model number, based on the insulation and size of your property, will probably never peak over 3kWh.

This is something that I’ve wanted an answer to for quite some time, and I’ll do some research this week, and hopefully update this comment with additional clarity.

Andrew Scott 19 January 2021 - 18:41

Regarding the ratings of heat pumps, what is classed as an 18 kW heat pump has a maximum ‘theoretical’ output of 18 kW of heat. Obviously in optimum conditions, and due to the COP, the input energy will be much lower. We have a groundsource heat pump rated at 6.5kW, and the compressor motor which is the majority of the load is a 2.2kW, drawing approximately 1.5 kW in operation.

Mars 19 January 2021 - 21:49

Thank you Andrew. That makes sense. Thanks for the clarification.

LJA 20 January 2021 - 14:12

Thank you both 🙂
That’s really helped to clear that up for me!

Julian C 20 January 2021 - 20:17

Links to note on 8th Jan. Thank you. I have since been talking to a different ASHP supplier / installer. Having done the demand and loss calcs he is proposing removing the oil boiler completely and installing a 16kW Daikin HT system and a new h/w tank. Higher price (but only by £3k) but I like the idea of no oil. Also no radiator changes which my wife very much prefers. Keep up the information and good work. I am only upset by how tidy your place is compared to mine 🙂

Mars 20 January 2021 - 21:18

That’s brilliant Julian. Sounds excellent. Please keep us updated on your progress and definitely let us know when the pump is installed. Good luck!

Paul Coathup 29 January 2021 - 23:46

I am in the process of designing a new house approximately 300m2.
My preference is to install a ground source heat pump with a surface array but unfortunately I don’t have sufficient adjacent land available and vertical bore holes are looking prohibitively expensive.
Does anyone know if it is possible to combine an air source heat system with a ground source system to provide the warm supply water to the compression heating system. ?
I hope this question makes sense to someone.
Thanks Paul C.

Mars 30 January 2021 - 09:09

Thank you for your comments John. I’m limited in my technical knowledge and know very little from a practical perspective about GSHPs.

There are some knowledgeable people that follow us here and on the YouTube channel, so maybe they’ll be able to cast some insights.

Can I suggest that you also post your question here too:

Andrew+Scott 30 January 2021 - 12:27

Hi Paul,
We have a GSHP, and despite not having sufficient land for a ground array were fortunate to have a small stream which we abstract from to provide our heat source. I am struggling to understand why you would consider combining an ASHP and GSHP. Both can provide the source of heat for underfloor / wet systems, unless you mean to have both systems with the ASHP assisting the GSHP due to limited ground array?

Paul Coathup 30 January 2021 - 18:49

Hi Andrew,
Yes, you have the gist of my question.
Is it feasible and realistic to combine an undersized ground array with an air source system ?

Mars 30 January 2021 - 19:23

Very keen to hear the answer to this.

Andrew+Scott 30 January 2021 - 22:34

Having worked in process engineering for many years, there is, in theory no reason why you cannot use both a GSHP and ASHP on the same heating system. The issue will be finding a supplier to design and commission a suitable control system. In essence, you have a warm water heating circuit on which your building is imposing a heat load or demand. This requires a heat input to maintain a temperature set-point. A control system with temperature transmitters on both the heat source inlet and outlet connections will determine if the boiler is increasing the circuit temperature at a pre-determined rate. If the programmed conditions are not satisfied, i.e. inadequate heat input, then it will demand a second heat source to assist. This will be the case for commercial properties with boilers, but my experience in this sector is very limited. To a control system designer would be a simple process but really you need to find a standard heating control system on the market, as bespoke control systems will most likely be prohibitively expensive. I will do a bit of research, and post a comment.

Andrew+Scott 30 January 2021 - 22:59

This article is worth a read on cascade boiler control systems. More for commercial systems, but the principle is commonly used.

Andrew+Scott 30 January 2021 - 23:05

Here we are. This is an off-the-shelf solution, but the system design will need careful consideration. It will need a heating engineer rather than a plumber!

Andrew+Scott 30 January 2021 - 23:36 Reply
Steve Jewell 31 January 2021 - 08:32

We recently installed a Panasonic 7.1kw ashp ( split unit) in a log cabin at the bottom of our garden. Very quiet and mostly warms the 48sqm cabin ok. As it mainly a garden office , it isnt well insulated, roof and floor insulation plus d/g, but only single skin 70mm thick logs. It is wifi controlled etc and alexa compatible. Too early to feedback running cost data. Issue we have is the unit sometimes shuts down before reaching temperature . The power light starts to blink and the vanes close up. Anyone got any ideas what might be the reason, before I get the installer back and potentially get the runaround. Thanks.

Steve Jewell 31 January 2021 - 13:55

Maybe answering my own question. The external unit is going into defrost mode which apparently can last 30 minutes. We are seeing a noticeable drop in temp during that time. We have been recommended to leave in Heat mode rather than Auto and to set the temp to a couple of degrees above desired temp to allow for the 30 min “ no heat” temp drop. We will test to see if this holds true but may be helpful for anyone thinking of heating/ cooling their conservatory etc. Steve

Douglas D 31 January 2021 - 15:55

Hi, We have an LG 12kw, HM121M U33 ASHP in a new 4 bed, 2500sq/ft house, underfloor heating on ground floor and radiators upstairs, it also provides the hot water. I work overseas a lot so there is only one person living there and underfloor heating is set to 21degrees. For the last few months it has been costing around £300 a month on Octopus tariffs , 14.6p kw/hr I think. The downside is the house although very well insulated does not feel very warm and the floor slab not toasty underfoot and my wife is scared to turn it up higher due to cost. We moved from a lager house last year which used oil central heating, also underfloor, and it felt warmer and was much cheaper to run although less well insulated. Really disappointed so far, are we doing something wrong.

Mars 31 January 2021 - 22:33

There appear to be issues with LG ASHPs. Not good, and not the first report of these pumps just not getting the job done.

Sam 31 January 2021 - 22:30

Hi Douglas
Like you I also have an LG pump , in a similar size property, with which I am hugely dissatisfied. Furthermore, May I ask you if yours emits a horribly irritating buzzing sound when it’s running? This is now the soundtrack to our life in this house to the extent we have to have the tv up loudly to drown it out, and are unable to sleep in our master bedroom, having instead to move into a spare room – hopefully only until the warmer spring. At the point of investigating if it’s possible to change system to lovely cheap, quiet gas. Sorry environment, but my standard of life is also important. Be interested to hear if also an issue for you?

Mars 31 January 2021 - 22:35

Completely understand your frustrations Sam. It’s ridiculous how noisy your pump is and that it’s not heating the house, and not surprised you’re considering shifting to gas.

Douglas D 1 February 2021 - 06:10

Sam, I don’t think it makes much noise but can’t be sure, I’ve only spent 19 days there since we moved in last July! I think my wife would have mentioned it if it was but it is behind the garage and not really close to any living areas tbh. I’m with you on the gas though, unfortunately there are only 4 houses and the builder did not bring gas in to them so now not possible really. My wife sent me all the bills last night and I think over the year it should end up being around £2000 (£160 a month) to run the system which is not as bad as the current £300 a month seems. She spoke to next door last night and they’ve just had a £400 bill so feeling lucky now 👌

Pavan Chaudhary 1 February 2021 - 11:17

Hi There! this website has been so hard to find but am glad you set it up! Long post alert as i am really stuck!

Am in the middle of a refurb/rebuild of a 1930’s semi in London. It will be 300sqm over 3 floors when finished with a 50sqm annexe. I am looking at ASHP, MVHR as well a VRV system and solar PV/thermal. (I have also thought of installing a gas boiler as a backup system for when its really cold)

Windows are triple glazed or double with blinds with u values in the 1.4 region and the rear of the property faces west. Heating in the house will be under floor to ground floor and radiators everywhere else. i have been recommended a NIBE 16kw unit by two installers. my concern is that the NIBE unit i am told experiences performance issues in low temperatures.

i tried (miserably) to carry out research and know the LG has a really bad cloud platform. I have been told about a new Vaillant arotherm unit by another installer which uses r29 refrigerant. does anyone have knowledge of NIBE or Valliant or another.

I am also worried about noise levels and the struggle to heat in lower temperatures as my father feels the cold the most

Thanks or reading and I would appreciate comments good (or bad!)


Sam 1 February 2021 - 13:08

Hi Pavan, avoid the LG as it has a horribly noisy buzz when working hard, and if I had any choice in the matter (it was already installed in my new build) I would chose gas for the economic, quick and easy warmth it allows. Out of interest, what is a bad cloud platform that you refer to regarding the LG?

Mars 1 February 2021 - 22:17

The cloud system probably means that the data generated by the pump goes online where you can access it, or you can control the pump remotely via your internet connected devices like phones and tablets.

This is a feature, in my opinion, that is really lacking in ASHPs (ours included), especially at a time when our homes become ‘smart’.

Pavan Chaudhary 16 February 2021 - 17:10

i head the same about decibel levels. am going to be acoustically insulating bedrooms to avoid this

Mars 1 February 2021 - 22:27

Thanks for the post Pavan, and your refurb sounds very exciting. I don’t know much about the Nibe or Valiant. Have you not considered an Ecodan, which is probably the most popular ASHP in the UK?

Most ASHPs should not struggle with UK low temperatures if they’ve been sized correctly for your property and have been commissioned properly. From what you’ve described, you should be more than fine maintaining temperatures at 21C+ with the right pump.

Also, when speaking to installers, ask them about the physical size of the pumps and how much space they need around them. That’s important. Don’t box them in.

And make sure your get a hot water cylinder with a buffer store.

To get more answers to your model questions, I’d suggest you post your question on our YouTube channel where there’s more diversity when it comes to ASHP users:

Robin Wilson 11 February 2021 - 23:35

Hi Pavin. I would agree with Mars that you should take a look at the Mitsubishi Ecodan systems. We’ve had one in (what was) a new build house for 11 years now and I really can’t complain that much about performance. Cost wise we have a monthly average bill of £250 for electricity for a north facing 4500 swift house with a lot of glazing. Our 14kW system keeps the house at 20-21C through the year. We don’t have any secondary heating source. Sure, there are a few days a year when it struggles and it only gets to 19C, but you can always put in a jumper! Maintenance on average is about £120 per year for a service from a recognized Mitsubishi dealer. Like other posts have said, find a good installer with a lot of experience on both heat pumps and air conditioners – they are remarkably alike. There have always been cowboys jumping on the ASHP band wagon with new developers. Ecodans aren’t noisy – not that you’d want to locate one in your living room, but if you’ve decent double glazing and you can locate the pump somewhere out of the way, you’ll never hear it – put vibration isolation under it as sometimes the noise you hear is vibration transmission through your walls via the surface the pump sits on.

Mars 12 February 2021 - 07:49

Thanks for sharing your experiences and insights, and a great point about potential vibrations. Do you UFH or is it all rads?

Sam 12 February 2021 - 08:21

Hello, what is vibration isolation and where can I get it? We’ve had to abandon our master bedroom due to the terrible noise.

Mars 13 February 2021 - 08:29

Hi Sam. I’m assuming you’ve had no solution or progress on your ASHP situation. Can you please remind me if LG came out to look at the pump?

Sam 13 February 2021 - 14:20

The pump is now heating the house really well after the fitter made several visits and tweaks, so that’s great. The bills we can do nothing about, and have made our peace with. Hopefully, 6 months after moving in, our solar panels will finally be activated at the end of Feb, and will help a smidge with costs.

But the noise is still a major issue.
LG visited and implied we should have bought Mitsubishi (” They’re Japanese and LG are, well, you know, Korean so…”) which wasn’t a particularly helpful response.
At times it runs with a soft whirring but often, especially in the cold, there is a persistent high pitch buzzing which drowns out the TV and results in us sleeping in a different bedroom when it’s cold. It’s just a really irritating soundtrack to our daily lives.
I will try the vibration isolation mats that you mentioned and have seen pump surrounds that claim to reduce noise problems.

Does anyone have any experience of these structures? Do they help noise within the house or issues for neighbours instead? Any recommendations or suggestions very gratefully received.
Looking forward to the milder weather next week,

Mars 14 February 2021 - 08:09

That response from LG is unbelievable Sam. Wow. Regarding the noise, I recently made contact with a heating engineer that deals with LG issues and mentioned your case to him. He asked if he could contact you to see if he could resolve the noise issue. Let me know if you’re ok with me passing your email address over to him so he can make contact.

Sam 14 February 2021 - 08:55

Wow, I can’t thank you enough, Mars. That’s so incredibly kind. Yes, please do pass on my details. Sam.

Pavan Chaudhary 16 February 2021 - 17:19

I did look at the Ecodan and was quoted for it however post covid i have been told mitsubishi have a massive supply issue and have basically upset a number of installers. I’m using a really good installer who was happy to listen to my 101 questions! Their advice is to ensure there is plenty of space around the ASHP. it helps i’m rebuilding everything from scratch so i can move whatever i need to to suit. thanks for the idea on the vibration isolation!

Pavan Chaudhary 16 February 2021 - 17:08

update for you all guys and sorry i have been so quiet. after posting this i disappeared down a hole as progress on the build really took off! will be responding to everyone now.

Mars 16 February 2021 - 21:35

How’s the work progressing Pavan?

Pavan Chaudhary 16 February 2021 - 17:45

So MVHR ducting is going in this week which was a wonder to finally see and our windows are in so no more layering up on site! Scratching my head as to what to actually buy for our cylinder! I have been advised to go for a size of at leas 300l and i have looked at the Vaillant Unistor. i have been recommended one by a company called worldheat also. can anyone guide as to what kind of cylinder I will need, am installing a vaillant arotherm with system boiler, solar PV solar therm

Mars 16 February 2021 - 21:37

We got a 300l tank (will check the brand in the morning) with a 100l buffer store. Will you need a buffer in your set up? Are you also putting in PV panels?

Joven Ruthford 2 February 2021 - 13:52

I think It’s just an observation at this point, but over the course of the coming year, I will look into this more closely and determine whether this correlation is accurate and precise.

Mars 2 February 2021 - 15:41

That would be great Joven. Look forward to seeing updates.

Lucy 4 February 2021 - 13:43

Whilst there appears to be many different heat pumps available, I have yet to find any impartial information available comparing how well the different air pumps work; the few reviews I have seen appear to have a commercial interest.
I’ve contacted Which? but currently they don’t have any plans to do a review. However, the more people that ask, the more likely they will do one.

Robin Wilson 11 February 2021 - 23:41

Has anyone any long term experience with ASHPs. I’ve an 11 year old system now and just had a failure due to a cooling coil leak causing the machine to end up as a block of ice and an uncomfortably high bill to fix. Proponents of the technology say it’s good for 20 years + but system leaks and compressor failures are high ticket items and I need to know the time – like with your car – when it’s better to change the pump than face big bills each year. Thanks

Mars 12 February 2021 - 07:55

Our pump is only two years old and the life of the unit is a major concern. I’ve spoken to a few engineers about this, and they all say the compressor (the most expensive component) should last 10-15 years. If it does break, it’s how it breaks that affects the system. If the refrigerant gets out, things get even costlier. There are far more experienced people here that can comment on ‘regular’ failures going forward.

Have you had your ASHP fixed?

Julian C 12 February 2021 - 08:38

Has anyone looked at the control system to link to agile tariffs like Octopus? Only works with some ASHP manufacturers so far. I’m looking at Daikin ASHP which is covered yet, but is in development. Looks interesting to keep ASHP running costs down.

Mars 12 February 2021 - 08:40

I came across this about a month ago, and generally people online are really impressed. I’d probably send an email to Homely and see which ASHPs they recommend.

Our second winter air source heat pump experience » My Home Farm 13 February 2021 - 10:05

[…] halfway through our second winter with the 18kW Caernarfon air source heat pump (ASHP), and it’s time for an […]

Kathryn Cousens 14 February 2021 - 16:50

Hi , I’m so glad that I found this site, as have felt very alone in trying to find out from other users about how to get the best (if possible) from our heat pump system. Moved into new built bungalow in Kent in November, previous heating systems have always been gas boilers. We are shocked about the amount of engery we are using and the cost after down sizing from our previous 4 bed house. I appreciate this system is greener but it is so much more expensive to run, and not user friendly My main moan is that we have been told we can only use the hall thermostat to alter the heating , so we dont have any flexibility to when it comes on (we turn the thermostat down at night) . I want to put in a smart or programmable thermostat. Can anyone suggest a make that would work ?? The system we have is a Samsung Air to Water heat pump. But dont know how to find what model or what size it is. HELP. Thank you.

Julian C 14 February 2021 - 18:50

Hi Kathryn
My view would be “call out the installers”. There must be a warranty and support for several years. I would have also expected some timer control on the ASHP itself. I’m sure Samsung ASHP are connected to the internet so there must be an app you use to control. Or contact Samsung directly. I’m sure they will be helpful

Mars 14 February 2021 - 22:06

Good point Julian. There should be a control panel for the ASHP somewhere Kathryn. If you do, you’ll be able to control the pump and change settings.

How old is the pump? Do you know?

Kathryn Cousens 14 February 2021 - 22:13

Thank you for your replies, yes there is a control panel but again we were told not to touch that and only operate the system via the hall thermostat. The Bungalow is newly built and does have fantastic insulation. I just want to get up to a warm house (but not by having it on all night) so thought a programmable thermostat would be the way forward.
It is a learning curve as you said Mars and I will speak to the installers to get more advice. Thanks for help.

Mars 14 February 2021 - 22:26

There are plenty of programmable thermostats on the market. Your pump probably has weather compensation as a feature, and once temperatures go over 6C, running costs drop massively.

Unlike other forms of heating ASHPs do require some knowledge and thought.

Please ask questions and we’ll answer what we can.

We have another winter video coming out this week.

Can you please share your daily average electricity consumption and give us a rough idea of the space you’re heating?

Mars 14 February 2021 - 22:02

Welcome Kathryn. You’ve joined the ASHP world at a bad time because the weather’s been horrible. You’ll learn to optimize it and reduce your costs. Deep breathes.

Is your bungalow well insulated?

As for the thermostat, there’s loads of ways of dealing with it. Unlike gas, turning the thermostat up or down doesn’t cut consumption. I know it’s crazy, and it involves a mental mind shift. To save power, you need to drop the flow temperature, and that’s why I asked about your insulation. If you’re not leaking heat, you can turn it down to say 40C or even 35C if you’re well insulated and it’ll still keep the house warm, but use a lot less power.

Do you have TRVs on all your rads, and are letting the ASHP run 24/7?

Claire 14 February 2021 - 22:11

Hi, interesting to find this, thank you as it will be most helpful I think.
We had a 15kw Vailant Aerotherm fitted Sep/Oct 20, in an old cottage we are refurbishing. We knew it wouldn’t be the best in terms of efficiency whilst we are still working on replacing draughty doors and windows etc. However like others here we were shocked at the £1000 electric bill for 3 months. So have now turned most rads right down and decreased temp from 20 to 16 but as I sit at a desk all day working from home it’s mostly not warm enough. We are playing about with it and monitoring consumption at the moment but the vailant engineer set the temp and told us to leave it running. To be fair it’s probably not too bad considering how draughty the house is currently but in warmer weather I struggled to sleep as upstairs was too warm. It also tripped the electric twice when the temp dropped below freezing and the installer tried saying we didn’t have the right electric supply (we fitted as he advised by him !) it hadn’t done it again since so we haven’t fought that corner with them as yet (they have been pretty bad). This last week we have been getting a warning saying water deficient ? Can’t find this in any manuals and the installer hasn’t got back to us as to what this could be, anyone else know what this could be or had the electric tripping problem? ( claims we need 2 32 amp cables and a 64 amp breaker, we have 1 32 amp cable and 32 amp breaker.

I will look at the electric rates from Symbio we are with Eon and think they are quite a high rate.

Thank you 😊

Derek Marsh 15 February 2021 - 19:28

Hi Claire,

I was sorry to read about your problems with your ASHP.
Mars has suggested that I try to resolve some of the readers issues.

Looking at the Technical Specification for your 15kW Vailant Aerotherm ASHP, it clearly states that both the start up current and the maximum normal operating current should be no more than 25 Amps. A 32 Amp circuit breaker and correctly sized cabling should therefore be adequate. As the outside air temperature falls the ASHP has to work harder and therefore draws more current from the electrical supply. If your ASHP should trip again I would suggest that you get a suitably qualified Electrician to measure the operating current using a Clamp Meter, preferably when the temperature is very cold outside. If the operating current is much above 25 Amps then I would suggest that you speak to your installer and/or the equipment manufacturer.

When you say that you have a warning message saying ‘water deficient’, is that the exact wording? Where are you seeing this warning message? I have had a quick look through some of the operating manuals, but since there are several it may be in one of those. If you can give me some guidance it may narrow the search.

Claire 17 February 2021 - 09:06

Thank you Derek your reply is very much appreciated. The warning message displays on the remote thermostat box. That is the exact phrase it displays (a little longer but that’s the term used) I can’t find it in any of the handbooks.

Will do what you said about the tripping. We had the hole house rewired so hopefully there should be nothing wrong there

Claire 17 February 2021 - 09:11

Sorry my partner has just said he thinks the warning was to do with the water pressure because at the time the system tripped he also found a small leak and thinks it’s all to do with this.
Thanks for your help, we are most grateful

Derek Marsh 18 February 2021 - 15:55

Hi Claire,

Thank you for your replies, I was beginning to wonder if I was writing messages just to help keep myself from getting up to mischief. (It doesn’t always work).
You obviously know what you are doing with regard to insulation and draft proofing.
In one of the manuals there is a warning for low water pressure, which would indicate a leak somewhere.
‘Check for leaks’ would have been a much better message than ‘Water deficient’. It may have ‘lost something in translation’ as they say. The important thing is that you appear to have located and rectified the problem.
I would not worry unduly about your system tripping out a couple of times, unless of course it becomes more frequent. When an electric motor starts it initially draws approximately 3 times its normal operating current. This is only for a fraction of a second and is perfectly normal and does not cause any damage. When electrical circuits were protected using fuses, this would be no problem at all. Modern electrical circuits are protected using circuit breakers, which react much quicker than fuses. It could be that on the occasions when your system tripped, the starting surge current was a little higher, or lasted a little longer than normal and hence caused the circuit breaker to trip. I hope this puts your mind at rest.

Derek Marsh 15 February 2021 - 19:52

Hi Claire,

I assume that you are not replacing your drafty doors and windows during the winter, so I would suggest that put masking tape over the cracks around your windows and draft excluder around your doors to keep warm until the better weather comes in the Spring. Not only will it give you a warmer home, but it should also reduce your energy consumption and give you a better feel for how your ASHP is performing. The better you stop the heat escaping the more efficient your ASHP will operate.

Claire 17 February 2021 - 09:07

I’ve bunged up and covered over holes where I can and used window cling on some windows while we await replacements. We keep finding new draughts though probably as i bung one up it’s finding it’s was out through an alternative but I’ll keep going, thank you

Kopernikas Green 16 February 2021 - 15:01

We live in a detached house of about 100sq Mtrs. Correctly our newish economy 7 storage radiators plus hot water costs about £1600 a year. Would an ashp save me money?

Sam 16 February 2021 - 19:46

Hi Pavan,

Just to pick your brains regarding soundproofing, if I may, how will you use vibration isolation?

I’ve contacted a couple of soundproofing companies
who offer ashp sound proofing surrounds but quotes are around £4000!!! These claim to reduce noise by approx 20 decibels.

Any suggestions gratefully received.

Mars 16 February 2021 - 21:40

That’s an eye watering amount of money for soundproofing. Wow. I didn’t realize until recently that the full interior of our ASHP is sound proofed. When it’s on, and I take a side panel off it’s remarkable how much louder it is.

Sam 17 February 2021 - 11:05

Hi Mars,

How interesting, are they made like that or was that done by someone? Which make is it?

Like you, I had no notion that it would cost anything like that!

Mars 17 February 2021 - 13:59

I genuinely don’t know if they’re all made like that. We’re working on a new project, which we’ll unveil in the weeks ahead, and that’ll hopefully provide us with a platform to get these kinds of questions answered.

As an aside, you should have a received an email from Bob today about your ASHP – if there’s anyone that can make something happen with LG, it’s probably him.

Sam 17 February 2021 - 14:08

Hi,Looking forward to the new project that you have planned. Sounds intriguing but will no doubt be interesting and very useful.

Yes, I did and I’m so very grateful. What a kind man he must be.

Derek Marsh 17 February 2021 - 23:31

Hi Sam,

Whilst i am awaiting your reply to my previous message, I noticed that you had mention vibration and soundproofing.
Vibration is created when an object with mass is moved backwards and forwards or rotated. The Cooling Fan and its motor will cause vibration, as will the Compressor and its motor. Some vibration is to be expected, but it should not be excessive. If you are experiencing excessive vibration then it would appear that one or more of the above components could be out of balance. Try putting your hand on the outer casing around the ASHP to see if any of the panels are vibrating, particularly when the Compressor and/or Fan are running. Let me know what you discover.
Soundproofing should never be required for equipment designed for domestic use. What were they offering to do for £4000, soundproof your whole house?
Something vibrating will cause noise, as will equipment that is working harder will create more noise than if it is running lightly loaded. Hard surfaces reflect sound, whilst soft surfaces absorb sound. A photo of where your ASHP is installed would be useful.
If you have had a chance to watch the video I recommended, you will now be aware that the cold air being discharged by the Fan should be pointing away from your home. There should also be as much space as possible around the ASHP to allow for the cold air to move away and be replaced by warmer air.
It may pay for you to contact the noise abatement society and see if they could measure the noise level. If it is in excess of the quoted level in the Technical Specification, then you would have a case to go back to your house builder, the ASHP installer and the ASHP manufacturer for a resolution. If the vibration level appears to be excessive, you could ask the equipment manufacturer to measure the vibration level at various positions on the ASHP, and then to take the same set of readings on several similar ASHP’s to prove that yours are not excessive. If they cannot prove that your equipment is not defective, then ask for a full repair or replacement.
If they refuse to offer to repair or replace any defective parts, then write to them saying that you are not satisfied and if they do not repair or replace within a reasonable period of time that you will the matter to Trading Standards and Consumer Protection. In your case, since the equipment was already installed in a new build property, you may have to chase the builder, unless you have any warranty documents from the manufacturer.
Let me know what you discover.

Sam 18 February 2021 - 12:17

Hi Derek,

I was also pretty gobsmacked by the quotes for the soundproofing boxes! At the moment, because it’s above 4° the loud humming doesn’t happen as the pump isn’t working that hard.

I have no idea if it is faulty or not, but everyone I speak to insists we should not be able to hear it to the extent that we do inside our house.

I have managed to get hold of an LG sales brochure so I’m just checking to see if there us any definitive guidance regarding not placing the therma v under bedroom windows or next to the main living area of the house. I’m hoping someone from LG may contact me, and if they do so will possibly push down this route. It’s difficult though as there is no direct contact at LG unless it’s about a phone or TV etc.

I’d have to wait until a cold snap to get a decibel reading, but that is definitely a route I will also explore. To be honest though, just the sound of it running normally is causing me problems and at 3am this morning , I gave up and went to a quiet back bedroom.
The siting of it has always concerned me as, despite have a big open garden to 2 sides of the house, the ASHP has been fitted at the narrowest part of a courtyard. There is only 80cm between the front of the pump and a large, solid wooden fence and I do wonder if the noise bounces off this and back onto the wall? Bizarrely, the one room you can’t hear it in is the wall it is against downstairs; it’s as though the sound travels up and sideways. What do you think.
I really hate to keep complaining about it though; I’m just desperately looking for solutions.

Mars 18 February 2021 - 15:37

Just heard from Bob that you have an engineer coming out in March to hopefully sort out any problems and that he’s already identified some issues from the photos you sent. Hopefully your heating will be working the way it should be next winter and that you’ll be able to sleep at night. Fingers crossed.

Sam 18 February 2021 - 15:44

Hi Mars,

I just cannot thank you enough for putting me in touch with Bob; what a fantastic man he is.

Thanks to you, and then Bob, we now have the head of LG technical visiting us. He was really helpful and for the first time I am thinking we may find a solution and be able to get in with enjoying our new home, and sleeping at night.

Home Farm, Mars and Bob (from LG comfort solutions) you are amazing.

Hopefully, in March, I’ll be able to update you with a positive result and maybe this will help others in a similar position too.

Mars 18 February 2021 - 21:18

That’s brilliant Sam, and you’re welcome. We know how frustrating it can be when things with your dream home don’t fall into place. We’re just glad that you’ve been able to make some progress and that the technician from LG will be able to assess what’s wrong with your pump. Once they do, at least you’ll know how to fix and remedy it, without the need to buy a £4,000 noise suppressor. Looking forward to an update in March. We’re actually having some performance issues with our heat pump addressed the day after you guys.

Sam 2 March 2021 - 18:27

Hi Mars,
The LG technician attended today, and was really helpful and informed. He confirmed that our pump is incorrectly sized, meaning it has enough power to maintain temperature but not to raise it when temperatures drop below 4°.

He also expressed concern regarding the ridiculous siting of it.

He is prepared to put together a case for us to present to Omnie and the builder proving that it needs replacing. Unfortunately, it doesn’t seem much can be done about the siting now all the pipes etc are laid.

Whilst I am hopeful that his influence can lead to action, I am highly sceptical that anything will be done. I suspect we will have to pay a reputable company to do the work, with us then attempting to persue the matter legally, but I would be delighted to be proven wrong.

From what he said, it appears that under sizing of pumps is a very common problem, so I’d like to plead with people to be sure to use quality installers and suppliers, and to do thorough research if they decide to go down the ashp route. If you are buying a new build property with one installed, please be extra cautious!

I’d also like to thank Bob, from LG comfort solutions, for his continuing support.

Mars 3 March 2021 - 08:06

Hi Sam. I’ll respond in more detail later, but have a quick question. Do you have a MCS certificate for your ASHP, because I’ve discovered something very interesting. Please let me know.

Sam 3 March 2021 - 17:16

Hi, I’m intrigued! I have a commissioning certificate from Omnie ( which surprises me as shouldn’t they have noticed the upside down flow rate pipe when checking and signing off the system as in accordance with their installation instructions?!) But no MCS certificate – unless that’s the same thing? We have one for our solar panels, which aren’t working yet as the fitter disappeared/ went out of business but I don’t have anything that looks similar for the ashp.

Mars 3 March 2021 - 17:47

There’s an incredible amount wrong with your picture Sam. The commissioning certificate is not the same as the MCS certificate. When you get a chance, I’d suggest you call MCS and see if they have a record of your installation – it may just be that Omnie never shared it with you because it’s in their name or just forgot.

The long and short of it, is that on page one of the MCS certificate, there are details of an “Insurance Warranty Provider”. In our case, this is HIES (probably the same guys you have for your solar panels). If this was an MCS accredited installation, and HIES are the warranty providers, there’s every chance you’ll be insured to rectify the botched installation. Come to think of it, I’d also call HIES to see whether they have a record of your property – from what I’ve heard, HIES are incredibly helpful.

Sam 3 March 2021 - 18:08

Thanks for that very useful info, Mars.
I will get straight onto that tomorrow. Just checked the solar MCS warranty and it’s with home improvement protection so I’ll also contact them to check the validity of that one too.

Derek Marsh 18 February 2021 - 16:35

Hi Sam,

Thanks for your reply.
You don’t actually have to wait for cold weather to measure the sound level. Obviously it would be best if you can completely replicate the problem conditions, but you can get the ASHP to work harder by turning up your Thermostat up in your house whilst you carry out the test.
I have not seen any photo’s of where your ASHP is located, but it sounds as though it has been sited in the worst possible location. The cold air coming out of your ASHP needs to be dispersed as quickly as possible before it is pulled back into the ASHP and cooled even further. If the cold air is drawn back in it creates a vicious cycle, which leads to the ASHP having to work much harder, reducing its efficiency, increasing running cost and also increasing noise levels.
As a quick test you could try one of the following:-
Fasten an old blanket or something similar to the fence in front of the ASHP to try to dampen the sound.
As an alternative you could try sheets of foam or even old egg cartons, opened with the inside surface facing the ASHP. I won’t bore you with the theory, but a simple explanation would be if you throw a ball against a wall, the ball will bounce back to an extent, but if you throw the same ball against a blanket hanging on a washing line it falls almost immediately. I hope this makes sense and please let me know what you discover.

Dan 19 February 2021 - 10:22

Hi there,

I found your videos and in particular the comments from other ASHP owners very insightful. We too have an ASHP and solar panels – we are single source energy, so everything is electric for us.

We have recently moved into a renovated barn conversion, we are the first owners since it was converted, and one of the main selling points for us was the solar panels on the roof (small size, total size 2000kwh p/annum) and the ASHP – it was sold to us as the house would be more environmentally friendly and more economical. I really am struggling to see these are affordable.

We have had a smart meter installed at the end of August, so apparently the costs are based on actual readings.
September 20 – £53.03 – 322kwh – this is the price point I expected, after being sold a “more economical” heating source. But then it snowballed, Oct – £88 (538kwh), Nov – £93 (566kwh), Dec – £127 (775kwh), Jan – £163 (992kwh), and currently for Feb till the 17th, its £87 (533kwh) with 11 days still to go. What concerns me is I didn’t think we were big users of electricity but I’m really surprised at how expensive this is for just 2 people living there. The house is 129 sqm, and downstairs is all under floor heating.

We live in a 3 bed semi detached barn conversation, which is fully insulated above building regs.

We have the under floor heating set to 17 throughout, and usually the room of the house is about 19 degrees, unless its a cold day. We have the heating come on in our living room zone about 16:30 – 18:30 to 21 degrees. Wondering if it would be better to just set the entire downstairs to 21 degrees, but in my head if it’s costing so much to heat one zone to 21 degrees, if we set all zones downstairs to 21 its going to massively increase the bills.

We have a LG heatpump – I’ve seen in your videos you show graphs, unfortunately I don’t think we’re able to get insight like you have, or at least the builders never showed us how.

One final point, I think a lot of people have been able to offset the running costs of the ASHP via grants, but because the builders installed ours, I don’t think we’re eligible. As per above, I am really struggling to see how these are the future, given so far my experience is they are very expensive to run.

Sam 19 February 2021 - 10:40


Like you we have an LG heat pump, there are 2 of us, have underfloor heating, and like you, we were sold a new house with the promise of low bills for heating. You’re actually doing incredibly well as ours is closer to £300 a month during this winter, and for December we were freezing as the rooms just wouldn’t heat up above 16°. The rooms are warm now and we’ve just had to make our peace with the running costs. In our previous house we averaged about £60/ month on gas and electricity combined so I know we’re pretty careful with our usage. Welcome to the wonderful world of ASHPs. On the plus side, if anyone can help you get a better understanding of the system, it’s Mars at Home Farm.

Dan 19 February 2021 - 10:58

Thanks Sam – wow £300!! I genuinely have been thinking something is wrong with our heat pump, that or someone has plugged in a hotub somewhere ha. 16° – blimey! Did you get the builders back out, because that surely isn’t right. Like you I have been used to bills of £60-£70 for gas and electricity, so when was told we had solar and an ASHP I envisaged lower running costs than this, which is definitely not the case.

What I notice about ours is it takes a long time for the under floor heating to really get going. Though my partner has said that if the heating is on and she tries to take a bath, she only really gets luke warm water from the bath which obviously isn’t ideal at all.

Out of interest, with your control panel, do you have any way of seeing performance stats / usage at all?
What sort of kwh are you using a month then? It’s alarming isn’t it when you see the bills.

Sam 19 February 2021 - 11:23

In all honesty, we’ve had so many problems that we’ve have just decided to accept the costs as they’re in line with what other people’s seem to be. Yes, we also had major problems heating the house to begin with. Rooms can take days to get to temperature from a low starting point so now we just leave everything and don’t alter the thermostats. Now the weather is warmer is does add a degree a little quicker though so it might be worth getting the temps where you want them now.
We haven’t had that issue with the water though. It will only heat it to 50° but that’s should still be ok to get a hot bath.
Where is yours located and do you have noise issues, especially when it’s working hard? Our main concern is that we have to have the TV up loud to drown out the humming, and can’t sleep in our master bedroom due to noise ; it’s sited on a patio below.
Luckily, we have got someone from LG coming to investigate, but it would be useful to know if you can also hear yours from inside your house?

I haven’t found any way of pulling data from the control panel, but I’m not particularly techie. I don’t know how many kws we’re using as there’s nothing we can do about it so I prefer to just try to forget it. We also have solar panels but they still don’t work 6 months in, and we can’t be sure they’ll ever actually get sorted. Never thought I’d miss being a British Gas customer!!!

Derek Marsh 20 February 2021 - 15:44

Hi Sam,

Did you see my previous message about simple methods to dampen the noise.
If, as I suspect, it is proven that your ASHP installation is sub standard, I would be chasing recompense, not only for the additional energy that you have had to purchase, but also for the time, trouble and distress you have suffered. Being a grumpy old man, I always find that mentioning things like Trading Standards, Consumer Protection and the Regulator work wonders when negotiating with unscrupulous companies.

Mars 19 February 2021 - 22:31

The UFH and lack of hot bath water doesn’t make sense. I wonder if there isn’t a settings issue. We are never without hot water because our system prioritizes that. Something is saying to me that your pump’s not been installed and set up correctly.

It’s annoying, but the only way to try and get to the bottom of things is do some reading up on your system. Do you have a manual for it?

Mars 19 February 2021 - 22:27

Sam, when the LG guys visit you, make sure that they check all your efficiency ratings and ask them what flow rate your pump is set to. Also ask them how you can change that yourself. That is important to try and get your bills down.

Mars 19 February 2021 - 22:25

Thanks for the comments Dan.

As a quick question, what is your electricity tariff. You might want to consider a flexible tariff with a company like Octopus.

Like you, there are a lot of questions about ASHPs. As a technology, it definitely works, but I think they’re not always installed well and made to run efficiently.

The graphs are not available to all makes. Our manufacturer has a dedicated portal where we log in and get our data.

My recommendation Dan, is to try and read up on your model, and play around with the flow rate. If it’s at 45C, drop it 40C. That will save money, and your temperatures shouldn’t drop too much.

As for RHI. This was raised as a comment recently and I think you’re right. The builders get the RHI payments, which I think is ridiculous.

Dan 22 February 2021 - 10:35

Thanks Mars, Derek and Sam for your replies, I will take a look at them in more detail tonight and respond to any questions.
Along with our neighbour we have decided to get our ASHP serviced, despite only having lived in the property for 6 months. From the comments in this blog and the responses I have received, I have a small list of questions for the installers when they come over for the service. I’d welcome any feedback on them and if there are questions missing.

1. Is the ASHP sized correctly for our property size?
2. What wattage is the ASHP?
3. Does the controller allow the user to view stats / performance?
4. What is the flow rate / and how would I adjust it if I wanted to?
5. Is it under warranty still (the builder left us zero info on the solar / heat pump)
Can you recommend any other questions it would be worth asking?

A side question to yourselves, we have a small solar set up (2000kwh p/annum). We are wondering what we should do with the excess electricity. Should we register for an export tariff or should we invest in an Edi box that will convert the excess to heat to heat the water.
Our solar setup is very small, so we’re edging towards just exporting the excess and getting a small rebait every year, once we can work from the office again, during those summer months it may give us a small amount back. Welcome any advice here?

Derek Marsh 22 February 2021 - 19:18

Hi Dan,

I suspect that the builders will have registered the solar panels for the Feed In Tariff (FIT) payments, so you will not be able to claim, as you stated with the RHI payments for the ASHP.
I had my solar panels installed and paid for them myself, so could register and subsequently receive FIT payments.
What you can do for reasonable cost (£400 or maybe less), is install a device to give you hot water.
I assume you are at present getting your hot water heated by your ASHP. Do you know if your hot water tank (or heat store as I think they now like to call them), has an immersion heater fitted? If so, you should be able to fit the device that I mentioned above. The device (ours is from a company called Immersun, though there are others on the market) basically monitors your electricity supply to ascertain whether you are importing or exporting power. If you are importing power then it takes no action, but if you are exporting power, then it diverts this excess (up to 3kW) to a designated load. Our particular device starts diverting the excess power as low as 100W, up to the maximum 3kW. Obviously you will not get much benefit in the Winter months, since your ASHP will be utilising most, if not all, of the power produced by your solar panels. But Spring through to Autumn you will find that more of your excess solar generation can be used to give you free hot water. My wife and I (we have a bath or a shower at least once every month whether we need one or not!!!) find that we have sufficient hot water for our needs.
With regard to your other questions, I would chase the builder/agent with regard user/operating manuals for all your equipment, if they are not forthcoming I would mention Trading Standards, Consumer Protection or Regulator. Those words usually have the desired effect. If you have no luck then please send me details of your equipment (manufacturer, model etc.) and I will see if I can locate the manuals and e-mail them to you.
I would question who actually owns the equipment, since you have been provided with no information and no warranty details. You may find this a strange thing for me to say, but when solar panels first started to become popular, there where various companies offering a ‘rent a roof’ scheme, whereby they installed the solar PV equipment free of charge, and then claimed the FIT payments. The home owner received some free electricity, but the equipment actually belonged to the company who had it installed. I am not saying that is the situation in your case, but if I were you I would clarify the point. If it is the case, then they would be responsible for any maintenance and repairs.
As far as your questions on operating your ASHP are concerned, I would have to look at the manuals to be able to give detailed information, but I produced various details on how systems should operate, which you will find buried within this blog.

Andrew+Scott 22 February 2021 - 20:50

Hi Derek,
Regarding your comments about consumer protection, it is also worthy of note that under the CDM Regulations 2015 (Construction Design & Management) it is the legal responsibility of the Principal Contractor or the Principal Designer to assemble a Health and Safety File which must be passed to the building occupier on completion. This file must contain all instructions on how to operate and maintain every component for the lifetime of the building or facility. Therefore if you do not have any instruction manuals in paper or digital format, then you builder has broken the law.

Derek Marsh 1 March 2021 - 16:14

Hi Dan,

I’m afraid I gave you some duff information previously (my bad, as they say).
Apparently the Feed in Tariff (FIT) scheme was ended for new PV Systems in 2019, and was replaced with the Smart Export Guarantee (SEG), details of which you can find on the Ofgem website.
Hope this helps.


Derek Marsh 20 February 2021 - 16:44

Hi Dan,

Your costs are not too bad compared to Sam’s, though I suspect Sam’s system has been incorrectly installed and is not running efficiently. I have just written a long detailed explanation of why ASHP’s in particular struggle at low temps, which you should find somewhere below.
As things stand at the moment in the UK, gas is probably the cheapest form of heating, though not the most efficient and obviously not the most environmentally friendly. We pay approximately 3.3p/kWh for gas and about 15.3p/kWh for electric. Because we have solar panels (4kW system), our electricity consumption has halved since we had them installed 10 years ago, and we also use the excess energy they produce for hot water Spring through to Autumn and also to supplement home heating which has reduce our gas bill by 20% over the last 3 to 4 years.
The good news for you and Sam is that the warmer weather is coming, so that you will soon find that your bills will fail quite dramatically, and even more so when your solar panels start to produce more output. From my records November, December and January are the worst 3 months, high heating bills and low solar output. The last couple of years May has given the best solar generation, less clouds so more direct sunlight.
From a heating point of view electricity is quite an efficient fuel, since you are not blowing hot air up a chimney. Its cost relative to gas is the problem. ASHP’s have been developed to utilise electricity more efficiently
You need to convince your partner to take a shower rather than a bath, no more often than once a month, and only then if she needs one.
Joking apart, is your hot water heated solely by your ASHP or do you also have an immersion heater?
If you get me details of your system, manufacturer, model etc., I will see if I can locate a user manual and advise you on how to get the best from your system. Don’t worry, I have been setting up complex systems most of my career as an Automation Engineer.

Derek Marsh 20 February 2021 - 14:27

Hi Everyone,

Over the past several months I have been carrying out tests and monitoring the performance of our central heating system to ascertain whether or not an ASHP would be a good replacement for our ageing gas boiler.
The results have highlighted a number of issues, which when one thinks about it are common sense, but may not be so immediately, and are often difficult to quantify.
A number of readers have suggested switching off their ASHP’s for periods during the day or night, to save energy and in the process save money. I would strongly advise against doing so, since it is possible that under certain circumstances it could actually increase energy consumption and hence costs. I will explain in greater detail in a moment.
In a perfect Utopian world, logic would dictate that if we were to switch our heating off for 6 hours each day, then we would reduce our energy consumption and costs by 25%. Great, fantastic. In that case I’m going to switch mine off for 24 hours each day and therefore reduce my energy consumption and costs by 100%.
Unfortunately we live in the Real world, not the Utopian one.
Energy cannot be created or destroyed, it can only be changed in form. For best results it is therefore necessary to convert, transfer and retain this energy in the most efficient and effective manner.
Consider a hypothetical home, containing of 5 rooms all with a heat loss value of 50 watts per hour per degree centigrade temperature difference between the inside and outside. You probably think great, 50W/h I can live with that. Of course that is per room, so for the whole building we now have 250W/h. Not quite so great but still okay.
Now we come to the defining factor, ‘per degree Centigrade temperature difference’.
Now consider the table below.
Outside Temp. Inside Temp. Temp Diff. Total Heat Loss (kW).
20 20 0 0
15 20 5 1.25
10 20 10 2.5
5 20 15 3.75
0 20 20 5.0
-5 20 25 6.25
-10 20 30 7.5

If a 5kW ASHP has been installed on the home, the table clearly illustrates that by the time that the outside temperature has fallen to 0C, the ASHP is only just replacing losses, when working at full output. If you were to switch the heating off, even for a short period of time, the inside temperature would fall, because the losses don’t switch off. Even when the ASHP is switched back on, it would never get back up to 20C, because there is no ‘spare’ heating capacity available. It would only get back up to 20C when the outside temp increases above 0C.
It is therefore clearly apparent that if the outside temp falls below 0C, then the inside temp must also fall, the lower the outside temp then the more the inside temp will reduce until balance between heat supplied and heat loss is achieved.
The above example assumes a perfect ASHP that maintains its efficiency over its full operating range. This is not the case, as the manufacturers clearly state in their data sheets. Applying this fact to the above example, would mean that the ASHP would actually become less efficient even before the temp had fallen to 0C. The inside temp would therefore start to fall and would not recover fully until the outside temp increased to probably 4C to 5C.
The reason why central heating systems and in particular ASHP’s are slow to recover during cold weather, is because the heat loss is greater and the spare heating capacity is much lower.
Coming back to my first point, it is therefore inadvisable to switch off ASHP’s even for a short period during cold weather. Even turning the thermostat down by 1C in the above example, would only save 0.25kW of energy for each hour it is turned down, and would take a long time to return to the original temp when the thermostat is turned back up.
The best solution would therefore probably be to set the thermostat at the lowest setting consistent with personal comfort and do your best to improve draft proofing and insulation.
What is clear to me is that ASHP sizing and efficiency variations are important factors during the design phase and should be sized to cover possible temperature extremes with a little extra capacity built in. In the above example a 7.5kW or 8kW ASHP would have been a much better choice.
Just as importantly as the size of the ASHP is the size and/or type of the heating elements inside the home.
Water is used in central heating system as a good vehicle to transport the heat energy from the heat source (ASHP), to where it is required, radiators or Under Floor Heating (UHF).
It is of little use transporting the heat energy from the ASHP, if it cannot be extracted from the water at the point of use. The primary method of extracting the heat energy is by radiators or UFH.
The heat output of radiators is determined by their size, and the temperature of the water flowing through them. A typical double radiator 1200mm by 600mm, would have a heat output of 2000W (2kW) with a delta T of 50C. Delta T is the difference between the desired room temp and the water temp, so with a room temp of 20C, it would require a water temp of 70C to produce the specified heat output. As we know ASHP’s cannot heat water to 70C, so a radiator would not be able to achieve its full potential. In the above example the radiator would probably only deliver 1kW of heat energy with a water temp of 45C. This would again become a problem when the outside temp falls towards 0C.
The heat output of UFH is rated as Watts per square metre (W/m2). A typical installation would have a heat output in the range 76W/m2 to 91W/m2 at a water temp of 50C. Whilst the specified water temp is more compatible with ASHP’s, an installation in a room of 10m2 would still only put 910W of energy into the room with water at 50C.
In conclusion. If your central heating system appears to work well at outside temps of 5C above, but struggles at temps below 5C, then it would appear you have a sizing problem. But before you dash out and buy a new ASHP or replace all your radiators, check for drafts, see if you can improve insulation, check the flow and return temps of your ASHP. Ensure you have an adequate water flow rate from your pump, some are adjustable. Check for sticking or closed in valves and air blockages in the pipework that can reduce flow.
If all this fails, then think about moving to a warm country where you don’t have to worry about such things!!!

Julian C 20 February 2021 - 16:30

Mars, please can you talk a little about flow rate? Was this discussed during your ASHP selection process? The reason I ask is I was just watching your YouTube vid 2 and right near the end you discuss only changing one radiator. And then showing it. I noticed you, like me have 10mm micro bore pipes into/out of said radiator. My bungalow is like this for every radiator. And I wondered if your property was the same? We have 22mm pipes from the boiler thru the loft. But 10mm drops to each radiator. Many ASHP engineers run a mile. But three are fine with it. Putting a buffer tank between the external ASHP unit and the radiators. And a big pump around the radiators. To get the flow rate up.
Appreciate your thoughts and site discussions.
PS went to look at the Daikin Altherma 3H HT external and internal units today. Very nice

Derek Marsh 20 February 2021 - 23:58

Hi Julian,

I have just finished watching a boring movie. I know, but its what we are reduced to during lockdown.
So let me see if I can help answer your question, though I’m not 100% certain exactly what your questions is.
Since I don’t know your background I will try not to get too technical.
Correct me if I am wrong, but I assume that you are asking if 10mm micro bore pipes are large enough for use in an ASHP heating system.
The pipework in a central heating system performs one primary task, it guides the water carrying the heat energy, from the heat source (ASHP), to the end user (radiators), and also stops it leaking allover the furniture and floors and upsetting ‘she who must be obeyed’.
Without getting too technical, the quantity of water that can be pushed through a pipe is defined by the internal area of the pipe and the force (pressure) pushing it. A good example would be a syringe, if you have two syringes containing the same amount of water and you push one gently and the other one hard, the water dribbles out of the first one but squirts out of the later. You have still moved the same amount of water, the difference being the time element. In a central heating system the flowrate would normally be measured in litres per min (l/min).
For practical purposes we can say that water is a liquid and therefore cannot be compressed, so whatever quantity we push into an already full pipe, the same quantity will come out at the other end.
So, coming back to your particular question, you have a single 22mm pipe in your loft which is supplying a number of 10mm pipes connected to radiators.
The internal area of the 22mm pipe is approximately 380mm2
The internal area of the 10mm pipe is approximately 78.5mm2
The internal area of the 22mm pipe is approximately 4.84 times larger than that of the 10mm pipe, and can therefore be used to supply up to 5 radiators without affecting the flow velocity.
A typical central heating pump has a pumping capacity of approximately 25 l/min., so if 25 litres of water is pumped into the 22mm pipe, then approximately 5 litres will flow into each radiator if 5 are connected.
A typically sized domestic radiator holds between 5 and 10 litres of water, so in your particular system the water in each radiator should be replaced at least every 2 minutes.
Although you may not have a problem with flow rates, you may still have a problem in transporting sufficient heat energy from your ASHP to your radiators and from your radiators out into your rooms.
I wrote quite a lengthy description earlier today about the effects of water temp and radiator sizing etc. I would suggest that you read this post and if you have further questions then please write back. It would be useful if you could provide details of your present system and what your are planning to do.

Julian+C 24 February 2021 - 14:26

Replying to Derek’s note of 20th Feb. Thank you for your comprehensive note. I am a bit technical, so understand the points you make.
You make one point about one 22mm pipe can support approx. five 10mm piped radiators. Since we have 26 radiators around the 204m2 bungalow, I am correct in assuming there must be multiple 22mm pipe runs in the loft to support all these 10mm radiators?
The heat loss and radiator sizes for my home assume a 55C start temp. Assuming 22 C in bathrooms, 21C in living rooms and 18C elsewhere. This is driven by an 18kW Daikin Altherma 3 H HT ashp. A heat buffer between the ashp and the radiator system.
The calc suggests the heat pump (without separate electric heating) would cope down to -6C and consume 7344.8kWh for space heating.
So I have read your ashp sizing note and think mine is sized for all eventualities. I may have to change a few radiators – but will trial and see first – else Mrs Julian will hang me.
Given the information provided and the discussions here – I plan to take the ashp plunge. Perhaps I ought to video and send to Mars for inclusion on your site?
I have been in touch with Homely and they now have a Daikin solution – to track agile prices. I am currently on Octopus Go tariff – which according to my price tariff tracking app, is the best value (cheapest) for me currently – I am sure this will change with an ashp.
Thank you Derek and Mars

Derek Marsh 25 February 2021 - 10:25

Hi Julian,

Thanks for your reply, it is always nice to get some feedback.
I was quite surprised to read that you have 26 Radiators in 204m2. What size are they?
In the example I gave, 5 Radiators would maintain the flow velocity. If you were to connect 10 Radiators instead of 5, then of course the flowrate through each Radiator would halve.
This should still not be a problem, since your Radiators will heat up much faster than they are cooled by the surrounding air. Water is quite a good conductor of Heat Energy as is the metal Radiators, the limiting factor is the air in the room. Air is quite a poor conductor of Heat Energy, hence its use as an insulator in cavity walls. The air in a room is actually heated by convection, as the air coming into contact with the surface of the Radiator is heated, it then rises pulling colder air in to replace it. This is one of the reasons why rooms take a long time to heat up when the heating is switched back on.
It is possible that you have several 22mm pipes feeding different zones of your property, though it is also possible that you have only one 22mm pipe, provided that the flowrate to each Radiator is sufficient to meet the Heat Demand when all the Radiators are being heated at the same time.
As you are probably aware, I am still gaining knowledge and experience in relation to ASHP’s, but I was still surprised that an 18kW system has been proposed for your home, seems a little on the large side.

Derek Marsh 23 February 2021 - 11:29


Thanks for the information concerning CDM Regs.
Having worked as a Professional Engineer on large multi-national projects, it was a given that all manuals and necessary documentation would be passed to the client. I normally dealt with the technical side rather than the legal/contractual, so thankfully did not have to study the CDM Regs in detail.
It is one to remember for the future.

Andrew+Scott 23 February 2021 - 20:50

Thanks Derek.
Similarly I also worked as a Technical Manager for a construction company working within the Mining and Water industry sectors. As I undertook the CDM role of ‘Principal Designer’ for some projects, I completed a training course to gain the professional status of PD. However, I ‘progressed’ from this role in 2018 and to be semi-retired, to support elderly family members and have more time for hobbies, and assisting in technical capacity where I can.

Derek Marsh 24 February 2021 - 01:24

Hi Mars & Everyone,

I have just watched the video from that Julian recommended in a previous message, and I do feel it could be highly beneficial, particularly for large heat hungry homes. If, or when I do install an ASHP it is certainly something that I will look into in more detail.
Without wishing to sound like a wet blanket, I can think of a few points of concern.
Obviously you have to have a smart meter, which I think some of you have said that this can be difficult to get.
You would probably require an ASHP that has a slightly higher power rating than would normally be specified for your particular property. This would be so that the controller can raise the indoor temperature slightly, prior to shutting off the heating during the expensive peak period, and then bring the temperature back to the setpoint once the peak period is over. I know from reading your messages that some of your systems have been struggling to maintain the desired temperature, let alone have some spare capacity. Obviously if you have not had your ASHP installed yet, you can request a larger one, though probably at greater cost. Those of you who already have an ASHP installed, may not have this spare capacity in their present system.
If your ASHP struggles to produce sufficient heat and virtually no hot water, then this particular load controller (which is basically what this equipment does) would allow you to heat your water using the immersion heater at the lowest tariff.
The data shown in the video was for one day (probably chosen for maximum cost saving), I would therefore need to see data for at least 1 year to be able to estimate annual savings.
You would probably need to make some lifestyle changes, like no cooking during the peak period, though my wife bought a slow cooker and then a Crockpot for use during the day when our solar panels are generating.Running your washing machine and dishwasher during off-peak periods.
A concern for the future, would be the effect on off-peak prices as more people start to use this type of equipment. I feel certain that some of the generating companies are probably making a loss at some of the off-peak tariffs, but live with this to stay online for the peak period where they make their major profit. If the energy demand throughout the day becomes more even, then the peak prices may fall slightly, but the off-peak prices will undoubtedly increase.
If anyone takes the plunge I would be interested to see the results.

Mars 24 February 2021 - 21:05

I have a similar thought process Derek. For me, the peak electricity from 16:30 to 19:30 is a tricky one. We cook every night, and while we have a gas stove we do use the electric oven regularly too, especially on homemade pizza Saturday. Finding the balance is tough.

Julian C 24 February 2021 - 21:38

I can’t comment on the point about systems struggling to maintain temperature during v cold weather as I haven’t moved to an ASHP.
But I do know we have a lot to learn about agile tariffs. You will need a smart meter. Whilst you will pay more to cook between 4:30 to 7:30pm, there could still be benefits over the whole day for your ASHP. Data analysis will be key.
You will be able to balance your electric demand/consumption with an electric car and vehicle to grid (V2G). Charge your car up overnight on cheap electric. Use the car during the day. Return and use the remaining battery to run your electric cooker. Repeat. Build in solar PV. With Homely you will be able to manage the costs/CO2 footprint.
I think it’s an exciting electric future. I have a Honda e. ASHP next.

Derek Marsh 25 February 2021 - 17:55

Hi Julian,

I agree totally about using the battery on your e-car as an energy store, there is a community in Utrecht already doing so. This arrangement would be much more cost effective than a Power Wall.
A close friend of mine is an Engineering Manager with National Grid and we have had numerous discussions about the effects of wind and solar generation on grid stability. It is something that I feel many of the politicians don’t fully understand. Power generation is a balancing act, since supply has to constantly be adjusted to match demand within fairly close tolerances. Failure to do so can lead to over voltage trips or overload trips and subsequent load shedding. Wind and solar generation are not really controllable, and can vary quite rapidly, which can be particularly troublesome during periods of low demand. This is one of the reasons why a smart grid is being developed to help smooth out demand for electricity throughout the day.
There may come a time in the not too distant future when most the electricity companies offer a smart tariff, so that they can encourage (by price), time periods when they wish their customers to use more or less energy.
The idea of using the energy stored in your car battery to cook your evening meal would certainly be beneficial from most aspects.
As you say, it is certainly an exciting electric future. My main concerns would be that the necessary technology would need to be simple to use, cost effective, readily available and reliable.

Jitka 25 February 2021 - 23:55

Hi Mars,
We have purchased a converted barn (converted in 80’s). Its main stone walls are dating back to 18th century. There was no insulation’s on the walls or floors (solid concrete). It’s a 4 bedroom, with 2 kitchens, two living rooms, 2 bathrooms to run.
We have looked into lots of ASHP when purchasing this property as it was only economy 7 storage heaters. We went with Mitsubishi EcoDan 14kW with 210litre DHW cylinder. We have installed all new radiators, we have Warmup underfloor hearings in both bathrooms. We have put 32mm insulating plaster boards on the walls, 30mm foil insulating boards. The converted extension (we knocked through the main house to the workshop) will have 50mm insulated plasterboard with 100mm insulated boards between rafters (vaulted ceilings) and we’ve put 300mm rock wool insulation in the loft.
We have the heating set to be on 24/7 at 19degrees. My question to you is about the electricity usage. We were pretty shocked that our bills came to £350 per month, on average 2400kwh usage per month. I have spoken to our guys who installed it and as we have two zones for our heating (parents adjoining 1bed annex), my main panel allowed me to monitor and alter temperatures for both zones. But our heating was on all the time, even if temperature was reached. So they altered my panel to flow temperature only now. But we are finding that the 38degrees radiator temp isn’t heating the house enough now. How do you run ASHP in the most efficient way? Would you be able to advice on how to set up our system to get the heat we need but not paying £350 per month? Thank you! Love your house by the way

Derek Marsh 26 February 2021 - 13:08

Hi Jitka,

I know that Mars is very busy at the moment with a number of projects, so I will try to answer your questions in his stead.
Could you provide details of the period over which your average costs and usage values have been calculated.
Obviously energy usage over the Winter months will be much higher than the Spring, Summer and Autumn.
Could you provide details of the floor area of the property and whether you have double glazing?
Do you have Radiators in the bathrooms or just the Warmup UFH?
As you have no doubt heard many times before, ‘there is no such thing as a free lunch’, so although you are getting some ‘free’ energy from the outside air, it requires a quantity of ‘expensive’ energy to achieve this.
According to the manufacturers data sheets, your Ecodan is one of the more efficient ASHP’s on the market. On your control panel does it provide a value for Coefficient of Performance (CoP)? If so, what is the value at various outside air temperatures?
The higher the CoP value, the more efficient your system is working, though you should be aware that the CoP falls as your ASHP works harder when the outside air temperature is lower.
Although it is one property, the living arrangements that you describe are similar to a semi-detached house, with two separate families. So your energy usage and costs, will probably be higher, two bathrooms, two kitchens, more people using energy etc.
The Warmup UFH used in both bathrooms is, I do believe, powered by electricity, but because this electricity is supplied directly from the grid, where the cost is 14p/kWh to 15p/kWh, the bill can soon add up over a period of time. To reduce costs, if you have Radiators in your bathrooms then try switching the Warmup UFH off for a period of time and see what effect this has on temperature and energy usage.
Having the flow temperature of the water coming from your ASHP set at 38C, will help reduce your energy usage and bills when the outside air temperature is approaching 0C or below, but will do so by reducing the inside air temperature during cold periods. It may be preferable to set your ASHP controls to regulate the flow temperature to meet the heat energy demand of your home as it varies. As the outside air temperature falls the flow temperature will be increased above 38C, but when the outside air temperature gets warmer the flow temperature will be reduced below 38C.
Try running your ASHP for say 1 week using one method and then a further week using the other method and see what differences can be achieved. You will need to record the outside air temperature (which you can do from the internet), the changes in flow temperature readings, your energy usage and CoP values if these are available. If you then send this data to me, I will analyse the results and see if there are any improvements that can be made. Making hourly readings would be ideal, but longer periods would be acceptable, with a minimum frequency of once per day.
My e-mail address is:-

If you can provide the information I have requested then it may be possible to optimise the operation of your system.


Salman 2 March 2021 - 10:25

Hello, and thanks to everyone for sharing your experiences.
I am due to have an ASHP installed next month, and have not been advised what model/make yet.
I have a large 5 bed home, and after reading some of the comments I am starting to worry.
I would like to ask if it is feasable/sensible to install the ASHP in the loft, or even in the shed to shield it from very cold temps?

TD 3 March 2021 - 07:54

I am no expert Salman, but I don’t think an ASHP will work if installed in a loft or shed as it relies on the free flow of a large volume of air through the system to work. The air being drawn into the unit is at a different temperature to the air being pushed out of it. If the unit is in a sealed area, then eventually the air being drawn in will be at the same temperature as the air being pushed out and it will no longer be able to function.

Mars 3 March 2021 - 08:07

You’re spot on TD.

Mars 3 March 2021 - 08:04

Morning Salman. In quick reply, as TD correctly states, you can’t place ASHPs “inside” structures like sheds, lofts, garages, etc. The reason for this is that the pump will transfer what heat is in the air, leaving that space very cold, and then there’s limited heat in the air for it work efficiently. You need a lot of ambient air.

Install the pump outside, in a sunny area if possible, with lots of space around it so that air can move freely.

Most importantly, make sure the house is well insulated and get rid of drafts.

Get 2-3 installers to quote and see what size pump they recommend. If your pump is undersized, your house won’t heat. See Sam’s most recent comment.

Are you replacing an oil/gas boiler? If yes, the proposal should have a heat emitter guide that shows whether your current rads are capable of heating rooms.

Don’t rush into the install. Take your time and do the research. You only get one chance at getting it right.

ASHPs do work, but there are a lot of boxes to tick.

Julian C 3 March 2021 - 16:43

I’ve taken the drug! 😊. I’ve paid my deposit for the Daikin HT system.
I do need to add Homely into the mix.
But otherwise go go go. With the Mixergy cylinder.
No planned radiator changes.

Mars 3 March 2021 - 17:08

That’s brilliant Julian. Congratulations!

Very interested to hear about your Homely set up.

Did your heat emitter guide say that any of your rads needed changing?

Is there a proposed date for the install?

Julian C 3 March 2021 - 17:30

Thank you. Exciting.
I think there are 5 radiators that are slightly undersized. Mrs Julian is not keen on the upheaval of rad changes. So we will see how we get on and then see.
We may change them in the future to also get the flow temp down

Kopernikas Green 4 March 2021 - 14:46

Great info. I have used commercial heat pumps both in Dallas in Texas State for over 20 years. I have been pleased with the energy savings and efficiency. Thanks for sharing.

Clover Rayner 4 March 2021 - 17:21

Throughout spring and autumn, our ASHP operating costs were much cheaper than oil. The real test was always going to be the winter when there was less heat in the air and where the pump has to work harder.

Mars 4 March 2021 - 17:22

And how would rate your heat pump’s performance this winter?

Kev M 4 March 2021 - 19:14

Thanks Mars and others for sharing all your experiences. We’ve just signed up for an ASHP. We got 3 quotes and decided on a local company who seemed to know what they were talking about. It will be a full system install based on a Mitsubishi Ecodan 14kW as we currently have storage heaters. All radiators (12/13), no UFH. Our house is quite well insulated and we’re getting new windows and doors so in theory it should work. We have a couple of solid fuel burners as back up. It’s alot of money but the RHI will help a lot (we’re just on the 20000kW limit) and it will be easy to make savings against our current all electric. It’s not all about the money though; we will use less power/carbon and hopefully have better heating too. Looking forward to it (but not necessarily to all the disruption!).

Mars 4 March 2021 - 21:56

Wow, that’s brilliant. Congratulations. Do you have a date set for the installation?

Kev M 5 March 2021 - 06:55

We do. Full survey on 9 March, install 6 April.

Dan 5 March 2021 - 08:48

Hi guys,

Just wondering if someone could give me their thoughts on if our ASHP is the right size.

Our house is ~129.5 square meters, I’ve seen a few posts above talking about the wattage of the ASHP, I asked our installer and they have said ours is 7kW. I imagine its much more complex than “yes, that sounds about right” or “no, that sounds too small” but just wondering if anyone has any insight?

The back end of Feb was a bit warmer so we came in at about £125 for Feb. Bringing our total electricity bill for Dec, Jan and Feb to £415, and a total of 1,742kWh.

Would if incorrectly sized the wattage of the ASHP impact the bills? i.e. would it have to work harder than a more powerful ASHP?

Sam 5 March 2021 - 17:49

Hi Dan,
We recently had an LG technician come out to check ours. We have 2700sq ft and a 9w pump, which he confirmed is too small.
He did a heat loss calculation and worked out that when outside temps drop below 4° we were able to generate about half a watt to heat the house, which explains why it can’t raise the room temps during those weather conditions.
It’s quite a simple calculation, for those who understand such things, so it might be worth asking whoever designed your system what yours is.
Apparently, the problems many people report regarding pumps not working below 4° are due to incorrect sizing. Given the small price difference between different power pumps, I just don’t understand why it’s happening. We, no doubt, have a long legal slog to get this remedied, as it’s on a new build property. Hopefully, you won’t.
As to whether it would save you money, yours sounds pretty economical in comparison to most, to be honest, but I’d also be honest to hear other’s opinions.

Derek Marsh 5 March 2021 - 18:27

Hi Sam,

If you have not already done so, I would get in touch with Trading Standards and Consumer Protection, since it would appear that your ASHP is not ‘fit for purpose’. They may fight the case for you.
With regard to economy, obviously the larger the property the greater the heat loses, which is why it is important to insulate and draft proof. What did the LG technician say about where your ASHP is sited and the noise problem, or is that sorted now?

Sam 5 March 2021 - 19:22

Hi Derek,
Luckily we have a well insulated house, but I suppose there is always a calculatable amount of heat loss that is used for the standard algorithm?

He thought the siting of the unit was ridiculous, but agreed that now all the pipe works are fitted, despite the fact we have plenty of open gardens on 2 other walls, there is very little that can be done about it. He was also pretty critical of the fitting, given that the flow pipe thingy is upside down and so had no way of checking the flow to upstairs rooms to ensure it’s balanced.

He felt the noise was created by the fact that when its below 4° outside, the pump is working with the compressor at its highest possible output in order to meet the demand for heat. And it’s the compressor causing the high pitch buzz in the cold.

I’m hoping a larger pump, whether the company sorts it or we end up paying to have it changed, and then possibly building a false wall, with sound proofing inside, on the inside wall where the sound comes through, will mean we can get on with our lives in a warm, quiet house – just like most people. I’m braced for months of fighting, but will get there.

Derek Marsh 5 March 2021 - 22:29

Hi Sam,

I have just seen your message and cannot agree that your ASHP installation is acceptable.
Firstly, if the ASHP is within 1 metre of a boundary fence then it will have failed to meet planning permission requirements.
Installing a larger ASHP may not actually solve the problem, but in fact could make it worse. (please see the message that I sent earlier).
I would suggest that you check with your builder, which company actually installed your ASHP (check whether they are MCS certified), who decided on where it should be sited, and if it was passed by the building inspector. Try to get everything in writing rather than phone calls.
I would suggest that you also contact:-
See if they can inspect your installation and advise whether or not it is acceptable. An appraisal from a professional organisation will carry more weight than the ramblings of a grumpy old man.
If, what I suspect is correct, you need to get your system installed correctly, otherwise you will have high bills and continual problems that will only get worse. It should not be your problem to resolve, it should be your builder.
Hope this helps,

Derek Marsh 5 March 2021 - 18:00

Hi Dan,

Looking at the figures you have quoted, I would say that your ASHP is more than adequate for the job.
Have you suffered any drop off in indoor temps during the cold spells? If the answer is no, then your system is correctly sized and also working well.
On your system, 7kW is the maximum heat output rating under ideal conditions. In practice the true value will be slightly less. At maximum output, producing 7kW/h of heat energy, would require approximately 2.3kW/h of electrical energy.
From the data that you supplied, 1742kW/h over 90 days equates to 19.36kW/h per day or 0.8kW/h each hour, on average. Obviously some hours you will have used more, and some hours you will have used less.
To give a comparison, our detached bungalow (worst type of property for heat loss), is slightly smaller in floor area.
On the coldest day during the period that you specified, we used 100kW/h of gas at an efficiency of probably 60%, so in practice utilised approximately 60kW/h of heat energy. When the temperature was -5C outside, we were using 5kW/h of gas each hour.
For most of the time a 5kW/h ASHP would have been adequate for your home, though it may have struggled during the coldest days. A ASHP larger than 7kW/h would probably have been slightly more expensive to run due to higher loses in the slightly larger motors.
You should find that your costs will start to drop quite considerably, as the warmer weather arrives and your solar panels produce more output.
I hope this answers your questions, and I would much appreciate you posting your monthly energy consumption figures so that we can carryout comparisons of different systems to identify any problem areas.

Derek Marsh 5 March 2021 - 19:03

Hi Everyone,

For those of you lucky enough to have an ASHP, you may find this site of interest.

It gives details of the Octopus Agile Electricity Tariff, that some of you may find of use to reduce your bills.


Sam 5 March 2021 - 19:28

Derek, do you agree that 9w for 2700 sq ft sounds underpowered? Below 4° we can only just maintain indoor temps, and even in milder outside temps, we have to only increase temperatures in one or two rooms at a time. We can’t maintain upstairs and downstairs at the same time. The downstairs rooms have to switch off before any rooms trying to maintain upstairs can start to do so. Hope that makes sense!

Derek Marsh 5 March 2021 - 21:37

Hi Sam,

2700 sq ft is approximately 250 sq metres, so comparing the size of your home with Dan’s would indicate a 12 to 14kW/h ASHP would be a more appropriate size.
But from the data that Dan supplied, it would appear that for most of the time, at least, his system is not running at full output. In fact it may never have had to run at full output.
So coming back to your first question, a 9kW/h ASHP that is working efficiently, should be able to cope with temperatures down to 0C and slightly below in a home of your size.
Is your ASHP the one that is noisy and installed in a courtyard? If it is then this may be one of the reasons why it is under performing.
Let me explain.
Your ASHP extracts energy from the outside air. It is able to do so, even at temperature below 0C, because the refrigerant gas inside the ASHP is probably at -25C or below when it enters the Evaporator. The refrigerant gas therefore absorbs energy from the outside air as it warms up from -25C. In doing so it cools the outside air near to the Evaporator, so at some point the refrigerant gas and the air near the Evaporator would be at the same temperature, so no further heat transfer would occur. Obviously this is of little use since the ASHP would soon stop producing any hot water. So the clever designers decided to fit a fan, that would be used to blow this very cold air away from the Evaporator and replace it with cold air from outside. This solved the problem and the ASHP worked happily ever after.
Joking apart, this works fine whilst the very cold air is being blown away by the fan, and being replace by (warmer) cold air from outside. If your ASHP is in a relatively enclosed space, the very cold air, being more dense and heavier than the cold air, stays near to the ground and sticks around. Eventually this very cold air starts to fill the enclosed space, and will then start to be sucked into the ASHP by the fan. Because this very cold air has had much of the useable heat energy already extracted, it has very little left to offer. The ASHP therefore works much harder trying to extract sufficient energy from the very cold air, becomes noisier, uses lots of electricity (big bills), does not produce a great deal of hot water, and annoys everyone in close proximity and beyond. Sound familiar!
Did the LG Technician say anything about where the ASHP was located, or was he the one who put it there?
A quick test if you have a thermometer, would be to measure the temperature of the air going into the ASHP, the temperature of the air coming out and the ambient air temperature out in the open away from the ASHP.
If the air being sucked into the ASHP is much colder than the ambient air, then the ASHP is incorrectly sited.
Hope this helps. Please let me know what you discover.

Assuming comparable levels of insulation, your bills should be about 1.8 times Dan’s over the same period. If my memory serves me right, I think yours were quite a bit more.
Would it be possible for you to send me a photo of your indoor controls, so that I can see if any adjustments can be made to improve operation. You can send it direct to my e-mail address which is:-
Look forward to hearing from you.

Andrew+Scott 6 March 2021 - 00:04

As a comparison, we built a new well insulated house in 2016, 158m2 Our SAP calculation for DFEE (dwelling fabric energy efficiency) which considers all materials, thermal efficiency and heat losses is 55.63 kWh/m2/annum. i.e. 8789 kWh/annum or 24 kWh/day or 1 kWh/h. Obviously this is averaged, so does not indicate maximum heating demand, but does provide an example for thermal efficiency. The SAP was used by our heat pump supplier and their calculation suggested just under 7 kW. Their nearest unit was 6.5 kW which they said would be adequate as the calculation is based on worst case conditions. As a result, our heat pump copes well, and we find in average winter conditions runs for approx. 5 minutes every half hour, 1/6th capacity. When we experienced temperatures down to -5 C last year, we found it was running for about 10 minutes every half hour or 1/3rd capacity. So, if our average annual demand is 1 kW/h and in winter worst case we may require 2 – 3 kW/h, we could have managed with a smaller heat pump, but design always has a utilisation factor, as do air compressors and services plant, to avoid running at 100% capacity. In our case our utilisation factor would appear to be 3. I hope this will help with concerns over correct heat pump sizing.

Derek Marsh 6 March 2021 - 08:20

Hi Andrew+Scott,

Thank you so much for sharing your information, it is highly useful and much appreciated.
You appear to have the ideal setup, well insulated home, GSHP combined with Solar PV.
Your system would also appear to be well designed, installed and commissioned, which shows what is achievable when people do their jobs correctly.
I feel certain that if we all work together as a group, we will be able to help resolve the issues that some people unfortunately experience, due to the poor design and/or installation that they have suffered.
Thank you once again.

Derek Marsh 7 March 2021 - 22:38

Hi Andrew+Scott,

I would like to pick your brain if I may, since I don’t have an ASHP to play with.
I noticed that your ASHP runs for a certain period each hour dependent upon loading. I assume this is the compressor that is running? Does the fan also stop and start, and if so, how does it correlate with the running of the compressor? Is your water pump located within your ASHP unit or inside your home? How often does the water pump stop and start?
What kind of controller do you have and what information does it indicate?
I am assuming that your system is set up to control the temperature of one of the rooms, by varying the water flow temperature to keep the room temperature fairly constant. How is the temperature of the other rooms controlled?
Any information that you can supply would be gratefully accepted.
P.S. Please try to move discussion to the new hub if possible (say he, sending a message on the old system).

Andrew+Scott 8 March 2021 - 09:34

Derek, I have replied to your comment as a comment to my own article. This may not be appropriate, but I am a newcomer to using forums etc. Please ask if you need any further information. Cheers.

Mars 8 March 2021 - 21:49

Good evening Andrew. What I would like to suggest, and I can walk you through this, is for you to visit this link (and sign in with your username and password):

You will see an add topic button. Click on that, and add a heading such as “Our GSHP” or something that describes what you’d like to share and discuss and simply copy the same text you added as a comment to your article. I. can also do that for you, but please start the topic that’s started by you.

Shout if you have any questions.

Derek Marsh 6 March 2021 - 08:36

Good morning Sam,

I forgot to mention, if you carryout the test that I suggested, please ensure that you wrap up warm and wear gloves in case you touch any cold metal.
Whilst I was laying in bed last night I was thinking about your problems (I know it’s really sad, but it’s what I am reduced to these days), a further route would be the National House Building Council (NHBC).
This is an extract that you will no doubt find of interest:-
8.2.17Handover requirements
Detailed information and instructions shall be provided to the homeowner.
The pack of information provided to the homeowner should include:
 user instructions for the systems installed
 contact details for the manufacturer and installer
 key components installed
 a completed manufacturer’s certificate from an acceptable independent assessment organisation, MCS or suitable alternative
 a completed installer’s certificate from an acceptable independent assessment organisation, MCS or suitable alternative
 details of the fuel type and source
 maintenance and servicing requirements
 warranties and/or guarantees for the LZC technology.
You can find the full document at:-
Let me know what the temperature test reveals. If it is as I suspect, I may have a simple arrangement that could definitely prove that your system is incorrectly installed and poorly commissioned.
Are you or your partner any good at simple DIY?

Morgan 6 March 2021 - 16:12

Just started looking into ASHP and some of the observations above are scarey! We have just moved into a 1950’s ish detached home in rural Derbyshire. We were well aware changes would be needed. The house has recently been fully double glazed but that’s it so far as insulation is concerned. So obvious jobs initially is loft insulation, cavity wall insulation and under floor insulation beneath the original parquet. A radon survey is being carried out now and won’t finish until end of May so no building work of any sort until then. The insulation work will then be carried out regardless of the heating solution. At present an oil fired Aga is providing hot water (sort of) and two wet radiators upstairs. All other heating is dealt with (poorly) by wall mounted electric heaters and a lovely log burner stove in the living room.
No mains gas (or sewage) so it’s a toss up between oil, electric or alternative. We both got excited when first hearing of ASHP as an option and fully intend inviting firms to advise and quote. However the risk of paying a goodly sum of money to possibly end up with a noisy, inefficient system and suffering the travails experienced by some here is a worry. I don’t know of anywhere that I can even see and listen to an ASHP in action to at least allay the noise factor fear. I will need some convincing during my research because one way or another this house will have a central heating system to radiators installed before next winter. I don’t want it to be by an oil fired boiler but if needs must then……………
Fingers crossed it’s a quiet, efficient ASHP system but the guys that come here to survey, evaluate and quote better know their stuff or else it’s oil. As much as I want to be more green I cannot be cold like this next winter. 🤞

Mars 6 March 2021 - 18:32

Hi Morgan

The comments section on this post has grown to the point where messages and help requests have been buried. The good news is that we have built and launched a dedicated website to get these questions answered, and we would like to invite you to visit and join our new community and repost your questions there. You can do so here:

Sam 6 March 2021 - 18:37

Hi Morgan

Like you we were also cold this winter- watching TV in a coat and scarf- but unlike you we are living in a brand new, highly insulated eco-house WITH AN ASHP and spending £250+ / month on electricity. Unable to sleep in our master bedroom or enjoy our sitting room due to the noise, I don’t think I have ever loathed any device quite as much, and had certainly never given a moment’s thought to our heating before we moved to this “dream”house.
I won’t mention makes or system designers, as I suspect we’ll be going down legal routes soon.
If we wish to see a pump incorrectly sited, fitted and sized, then quite genuinely you are very welcome to visit us. Then, should you choose to proceed, you can avoid the pitfalls.
We’re Northamptonshire region.
Kind regards

Douglas 7 March 2021 - 07:34

Hi all, Can someone give details, photo, diagram of what would be seen as “incorrectly sited”, particularly from a legal point of view where you would be within your rights to have the unit moved at the builders expense.
I’d also like to know just how easy it would be to replace an ASHP unit with an oil fired boiler. Is it as easy as one out, one in?

Thanks, Douglas

Mars 7 March 2021 - 07:49

Hi Douglas

The comments section on this post has grown to the point where messages and help requests have been buried. The good news is that we have built and launched a dedicated website to get these questions answered, and we would like to invite you to visit and join our new community and repost your questions there. You can do so here:

If you could post your question there, I will be answer it there and have some videos you can watch.

TD 7 March 2021 - 09:25

Hi Douglas, I am no expert but I imagine it would be fairly straightforward to replace an ASHP with an oil boiler. The main challenges will be having somewhere suitable to install the oil storage tank and if there is sufficient space to locate an oil boiler safely where the ASHP is currently located. Most oil boiler manufacturers do external units with their own weatherproof housings. We are having an external Grant one installed shortly. If the boiler needs to be located elsewhere, (internal or external), then the costs will increase due to the extra pipework that will be needed.

Derek Marsh 7 March 2021 - 09:55

Hi Douglas,

In basic terms, an ASHP should be sited such that the cold air being discharged by the fan, can be mixed and dissipated as quickly as possible with the surrounding air. It is important that the colder air being discharged by the ASHP is not allowed to be drawn back into the inlet side.
Please watch the following video which not only explains correct siting, but many other aspects concerning ASHP’s.
As an example, if an ASHP was installed at ground level in an enclosed courtyard, the colder air being discharged by the ASHP would eventually fill the courtyard with colder air. This colder air would eventually be drawn into the ASHP which would cool it even further. If this process was allowed to continue the courtyard would eventually be filled with very cold air (which cannot easily escape), the ASHP would be running flat out, but struggle to produce any hot water.
As far as replacing an ASHP with an oil fired boiler is concerned, I assume that it would be quite feasible to do so. You would need to consult with a suitably qualified company to ascertain the exact requirements in your particular situation.
ASHP’s do work, and are particularly beneficial when coupled with Solar PV.

Douglas 7 March 2021 - 15:26

Thanks Derek, I’m currently overseas and will check mine when I get home (not soon!)

Morgan 7 March 2021 - 07:47

Hi Sam,
Unfortunately your situation was one of the horror stories I referred to and that has made us rather sceptical re ASHP. I truly hope you manage to sort your mess and go on to enjoy your dream home. Good luck.

TD 6 March 2021 - 17:50

@ Morgan. After having one team of specialists visit our old converted farmhouse and finally conclude that we would need two 13Kw ASHP working together, an upgraded electricity supply and virtually every radiator in the house changing, I sadly came to the decision that ASHP was not for us. Even with the available grant, the cost was prohibitive and I worried about the cost of running the system through the winter. Putting the green benefits aside, it just didn’t make sense to move away from our existing oil heating. Instead I have decided to get our 30 year old oil boiler replaced with a more efficient modern designed condensing oil boiler and at the same time have the system converted to use valved control on the hot water and central heating circuits. The old boiler has a stated efficiency of 70% (on a good day when it was new!!), vs a 93% to 94% efficiency for the replacement. The valved control system should also help improve efficiency as we won’t be heating the upstairs radiators by thermal action when running the system on hot water only through the summer. We used to heat our water in the summer by immersion heater on Economy 7 but I have calculated it will be lower cost to heat the water using the oil boiler.
Again putting green issues aside, the main problem I have with oil is the volatility in pricing. That being said I am shocked how much electricity pricing has increased for our area in the past few months. I always shop around, but even with the lowest cost provider I have found, our bill will increase by around 20% this year.

Mars 6 March 2021 - 18:32


The comments section on this post has grown to the point where messages and help requests have been buried. The good news is that we have built and launched a dedicated website to get these questions answered, and we would like to invite you to visit and join our new community and repost your questions there. You can do so here:

Morgan 7 March 2021 - 08:11

@TD I hear you. I really would like the ASHP to be a goer but I’m becoming less and less optimistic.

Morgan 6 March 2021 - 18:14

In addition to my first post I forgot two things. One was to say a thank you for access to an honest blog and the other to add that my property has been fully rewired and a connection for solar has been added.

Calum Swanson 7 April 2021 - 07:31

We fitted a Grant Aerona 11kw unit in our 220m new build nine years ago and I’m now on the third soft starter. The unit works great though it rarely goes below 0c in the Outer Hebrides and our electric bill works out around £180 per month. The house is all electric.
I’ve noticed a few people have Grant units fitted and wondered if any of you have also encountered this soft start issue?

Mars 7 April 2021 - 07:47

Thanks for the feedback Calum. Pertaining to the soft start, I’d like to recommend that you join Renewable Heating Hub:

Please register and pop your question there. We have a few Aerona users who may be able to comment. I can also point Grant UK to your post and they can offer feedback or solutions.

Green Leaf Air's Air Conditioning in Austin 10 April 2021 - 17:25

How does a heat pump affect my heating and electricity bills? Heat Pumps will raise your electricity bill – but lower your costs for other heating fuels.

Clover Rayner 20 April 2021 - 16:05

Most say that they’re not good enough to heat homes in the UK over winter because it’s too cold and wet. Throughout spring and autumn, our ASHP operating costs were much cheaper than oil. The real test was always going to be the winter when there was less heat in the air and where the pump has to work harder.

Mars 20 April 2021 - 22:01

Thanks for your comment Clover. What were your numbers like over this past winter?

I would like to invite you to join Renewable Heating Hub (our new sister website) where you can participate in our forum discussions and get answers to questions about renewable heating and heat pumps

Simon 7 May 2021 - 13:00

Please, please do not consider installing an ASHP if you live in any urban or village setting with neighbours close to you. We have recently had 5 new houses built next door, each with an ASHP, and the closest fan is a few metres from our boundary and approximately 8m from our back door. As we are in a quiet village, with very little ambient noise, the ASHP is a massive nuisance. It sounds like a loud fridge with a constant throbbing hum. We cannot hear it in the house with the windows shut, thank goodness, but with a window open at night, or when in the garden, the constant drone is infuriating.

If you value your relationship with your neighbours, please do not install one unless you really have the space to keep it well out of the way. We have contacted environmental health to register a noise complaint, so we shall see how that goes. When I talked to the installer about the surprising amount of noise, his reply was that ‘we would get used to it’!

The government is really pushing ASHPs. and it is going to cause no end of problems. We have only had to put up with it for a few weeks, and I am already on the verge of ripping it off the wall and setting fire to it. Goodness knows how noisy it is going to be over winter. I am dreading it.

If you live on a smallholding – great. If you have neighbours – no.


Mars 8 May 2021 - 14:09

Thank you for your comments and observations Simon. Many manufacturers are working very hard on getting ASHPs as quiet as possible, and it really does vary from model to model. What ASHP do you neighbours have? You may want to share your thoughts and experiences here on the Renewable Heating Hub forum where homeowners are discussing ASHPs and noise level:

Phil Martin 19 May 2021 - 23:04

I was just wondering if I had read your reiw correctly. On a day when it was not particularily cold, an average of 7C, you apper to have used 52Kwh of electicity. I have a decent sized detached house with two floors in an exposed and windy position. The house is a 1930’s house and has steel framed double glazing, and a lot of it. The cavity is not suitable for cavity wall insulation, so it is not a heat efficient house The units are old and let out a lot of heat. Our boiler is now over 20 years old. A disability means I have to have my house warmer than most. However we use about 11Kwh of electricity maximum a day in the winter running our home, which would translate into having to use about 40Kwh to run a heat pump. If it uses that amount of electricity to run, then that would cost us more to run a heat pump than it costs to run our gas heating and hot water in a very cold month. Have I misread your review? We will have to change our heating system in the next few years and I was hoping to have an air heat pump. Thank you!

Jill 28 May 2021 - 17:48

Hi all,
I hope this request for basic information is acceptable on this forum. I am at a very early stage in my research and others seem to be much further down the track.
I’m about to extend my 2-bed terrace house and am seriously considering replacing my mains gas CH with an ASHP. The intention is to install underfloor heating (water) and supplementary rads downstairs (would these be needed) and rads upstairs. This site has been very useful but I have a number of basic questions about how it all works.
How controlable / instant can the heat sources be? There appears to be a high emphasis on insulation. I intend to improve the overall insulation of my house, including changing the windows however I do like to have windows open to ventilate the house. With my gas CH (rads only) and combi boiler I simply turn on the heating when needed (or light the fire for a quick localised solution). Instant hot water comes from the combi-boiler without any water storage tank. The combi-boiler also ensures a high pressure shower. I can regulate the
areas of the house according to use.
How comparable would an ASHP be? Can I zone the underfloor heating so that it is not all or nothing? Can I get instant hot water?

I have a small garden and would like to screen the pump for aesthetic purposes. Would this impact on it’s efficiency?

As I say, mine is a 2 bed terrace so the pump would be close to the boundary wall between my and my neighbour. Is this likely to cause disturbance? Would I need planning permission ? I live in Wales.

Mars 28 May 2021 - 21:21

Thank you for comments and questions Jill, and I’ll be happy to help. On that note, the comments on our ASHP posts have become overrun, so we launched a new website and forum to better answer questions.

I’d recommend creating an account on the forums at Renewable Heating Hub and copying and pasting your question there to get assistance not only from me, but from multiple other homeowners:

Phil Martin 29 May 2021 - 11:28

Jill, you sound like you are in a similar situation to me. I have been doing my research too, and it would seem that the ASHP systems being marketed rely on the structure of the house as part of the heat store. (there is another more costly way of doing it, but it needs space) The house therefore needs to be well insulated, more than is possible with most of the existing housing stock. If you like to have your windows open during the day, the stored heat can be lost, and it takes a long time to get the house back up to heat. I have decided against it as I would need to supplement it with electric heaters. The author seems to use more in electricity running his heat pump than I would heating my house with electric heaters! So no instant heat, possible lack of hot water, and the heat pump could be noisy and should not be shielded. Read the Samsung website. My daughter did buy a new eco house that was built round a ASHP, together with a heat recovery ventilation system and a south facing roof with solar panels. That did work well, but the house was stuffy and not bright as they had only a few windows, and they would not open. They also had a rather large electricity bill! I hope that helps, it could cost a lot to buy, a lot to run, and not work the way you would like i! Phil

Clover Rayner 7 July 2021 - 15:23

If you’ve got an air source heat pump without solar you’re probably better off with more gloomy, overcast warmer days and nights that trap the heat because they’ll run are efficiently. At least that’s what our data is showing us at the moment for our pump and weather conditions.

Mars 8 July 2021 - 07:53

Thanks Clover. I agree with that. As an add on point, even without a PV system, sunnier days still tend to warm our house up even if it’s cold outside. Overcast nights are definitely better.

HMK 21 August 2021 - 17:21

In 2014 I purchased a house in Gloucestershire UK, took out the old smelly oil fired system and had an air to water heat pump installed with 6kw Solar PV, and a year later 2 Tesla batteries (which can be charged off the Solar PV and Economy 7 main tariff). Worked fine until last winter when the heat pump failed – heat exchanger leaked and lost all its F-gas (not good for the environment).
I won’t mention the manufacturer of heat pump as I am currently in discussions over it not meeting expected durability standards especially as the current version of the same model carries a seven year warranty.
I had a lot of trouble finding any heat pump engineer willing to look at my failed heat pump (my installer stopped trading a short while ago) and finally found a company that charged me £250 for a single visit to tell me what I already suspected.
I have lost some confidence in heat pumps as a reliable alternative to other heating systems that cost considerably less to install and maintain, and appear far more reliable.
I would be interested in hearing about air to water heat pump life expectancy from other owners and opinions / recommendations on the most reliable air to water heat pumps.

Mars 22 August 2021 - 08:23

Thanks for the comments and for sharing your experience. The lifespan of heat pumps should be over a decade, and from what I understand it’s the scroll compressor that fails. Refrigerant leaks like yours are rare.

Two things. I would suggest you copy and paste your comment as a new post on Renewable Heating Hub where you’ll get more answers from homeowners:

Secondly, I understand your reluctance to reveal the manufacturer publicly. Can you please email me the details – – because this the first gas leak failure we’ve heard and come across.

Ri 1 October 2021 - 21:30

I’ve had an air source heat pump now for 7 years have gone through all kinds of issues from impellors disintegrating to gas losses twice.
We did as manufacturers stated and insulated and sized everything correctly and were told you wont need that log burner! . Am glad I didnt listen the log burner had been a life saver .
When the impeller shattered the heat pump went like an old washing machine and didnt knock off , luckily a neighbout was passing and turned the main isolater off . Ok now for the nitty gritty , there good but usual cost over average year is 1600 pound to run , on oil it is around 1100 I receive around 850 pounds from my solar panels per year . I’ve taken the plunge to revert back to oil as my pump is beyond repair now and quotes are around 9k for a new pump . What annoys me is I’ve all the tanks inside so there ripping me off . Its times like this where the government should step in and make the manufacturers stop charging ridiculous amount for these unit .

HMK 2 October 2021 - 13:19


I wonder if this is the same manufacturer that I am having ‘discussions’ with at the moment?
Whilst I was very happy with my heat pump installed in 2014 up until Autumn last year, I started to notice it failing to provide the heat enjoyed in previous years, and by December it was obvious it was failing. Unfortunately my installer had ceased trading a few years ago so I started a search for someone to take a look at the heat pump.
That has taken until this summer to find a heat pump engineer willing to work on my manufacture of heat pump and when I finally did I was told the heat exchanger had failed and I had lost most of my gas. Re-gassing was not an option.
I was fuming as this part of a heat pump is supposed to last 20 years plus, so I contacted the manufacturer as I felt that this was due to faulty manufacture. Also the manufacturer was now providing a 7 year warranty on its products so I also made it clear that the product was not fit for purpose as it was not of expected durability under consumer rights regulations. My argument is that the heat exchanger can only fail in this manner if of faulty manufacture and as they are now saying the life expectancy of one of their heat pumps is now seven years, the life expectancy of my heat pump of the same model should have this same level of durability and not fail after just six years, or have they made modifications to the older models because of known / discovered problems with older heat pumps in which case this the product would again be not fit for purpose.
I am not mentioning the manufacturer as I am still in discussions with them. I had to go over the heads of the tech department / customer services as they were being smart a…s as they were ducking and diving and sending me around in circles. I found the names and emails of five senior managers including the UK CEO and included them in on my communications. That got a more meaningful response!
They have now sent an engineer to look at the heat pump and installation, who confirmed the previous engineers verdict that the heat exchanger has failed and the gas leaked into the circulating water so was probably vented into my house as I was experiencing air locks and bleeding the system. He also identified that the pressure vessel inside the unit had also failed, though my installation is up to required standards (they jump on any small issue to avoid responsibility) and has two more pressure vessels for DHW and heating system.
It will cost around 11K to replace my heat pump, as a pensioner I will have problems finding funds, so I am not going to roll over and take this sort of loss when I believe the product to be substandard. I have made it clear that I believe that they, the manufacturer, should make the necessary repairs. The future heat pump market is significant and very competitive. If they don’t take a significant level of responsibility for these failures I am going to provide honest and truthful comments on multiple social media platforms so people looking the install a heat pump will be well warned about the durability of this manufacturer’s products and attitude to customers who experience problems.
I am chasing their response to the engineers report (inspection was nearly two weeks ago) as it is starting to get cold (log burner will be lit soon, which I also decided to keep) but I would like a centrally heated house rather than having a hot single room and using expensive electric heaters to keep other rooms habitable / above freezing.
I would suggest following a similar complaints route. If you contact me directly we can share details of the manufactures of our heat pumps and if the same manufacture I can provide details of the senior managers to contact.
I am happy to talk with any other people suffering similar problems of defective heat pumps failing well short of expected life expectancy.

Richard 6 October 2021 - 18:23

Would be great to gave a chat over our issues although not sure how to do this

Mars 6 October 2021 - 18:25

Please head over the forums on where you can discuss this.

MDE 20 October 2021 - 23:38

Has anyone modelled the effect of a million homes in London or other large urban areas, operating ASHPs, replacing their boilers?

Bill Hume 25 October 2021 - 00:07

An interesting read! With a solid fueled stove which heats the living room, runs the central heating and provides the domestic hot water – from late October to mid-May typically, with full-price electricity providing hot water and comfort warmth over the rest of the year, and using mains water electric showering, I had hoped that a ground source heat pump (piping would be able to go under the back garden) would supply hot water, so as to replace the solid fuel stove should it develop a leak (as did its two predecessors, though this one has lasted nearly twice as long as the others did, approaching 30 years now). It’s clear that I need to start to measure and log lots of temperatures, meter readings and so on, so that data can be made available to prospective heat pump installers to help them with their sums! It’s less to do with saving money and more to do with when solid fuel is no longer available! Thanks!

Frances Griffiths 7 November 2021 - 21:50

We have had an LG heat pump in our 4 bed detached house since March 2020. We are very pleased with it. When we had a gas central heating system it took 12000 kWh per year to heat the house. Since we had the heat pump installed it has used just under 5000 kWh over 20 months. It was 3800 for the 12 months from April 2020 to March 2021.
We find it best to leave it on all the time at 20 degrees C. We turn the thermostatic radiator valves down in bedrooms we don’t want to heat, which is all of them really, as three are unoccupied and we prefer to sleep in a cool room with the window open.

We have solar panels on both the west and the east sides of our roof. Also a Tesla battery. This means that we produce nearly as much electricity as we use. We were about 1000 units short last year. Of course we make it in the summer and use it in the winter. The scientific world hasn’t yet come up with a domestic scale method of storing electricity from summer to winter unfortunately.

David Storm 25 November 2021 - 21:16

6 years ago we needed a new heating system in our large Victorian house, which has 15 big rooms, including 6 cellar rooms. Prior to the heating upgrade the cellars were left unheated, which made the whole house feel cold. We have stone walls, so no wall insulation, but we do have thick loft insulation. We have double glazed windows everywhere. Our old heating system was an inefficient gas boiler. Our new system includes underfloor heating in the cellar, with oversized radiators elsewhere. We run a 16kw Samsun EHS Monoblock Heat Pump, in tandem with a Vaillant Ecotec 30kw gas boiler. We also have a 4kw solar array and a solar i-boost unit, which diverts electricity to our hot water cylinder’s immersion heater (Dimplex 300l cylinder) when our solar array is generating unused capacity. The way our system works is the gas boiler heats the water and the heat pump runs the central heating at all outside temps above 3c (our installer recommended 5c and set the system up that way, but I’ve recently changed it to 3c as the heat pump is not struggling to warm the house at this outside temperature and Samsung recommend a switch-over at 3c). We are very happy with the performance of our heat pump, it has no difficulty maintaining inside temps at comfortable levels throughout our old and not well insulated house. However, it’s great to have the gas boiler to heat the water and run the central heating when it’s really cold outside. This hybrid solution works great.


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