Potential air source heat pump running cost issue

by Mars

When we installed our air source heat pump two years ago, all our running costs and calculations were based on electricity being sold at around 15p/kWh. We’ve changed electricity providers a few times to ensure that we stay under that financial mark, but that’s proving to be more and more difficult and I think that air source heat pumps are going to be put under pressure from a running cost perspective in the years ahead.

So let’s put things in context. Before our air source heat pump went in, we were paying £250 a month in oil (at 50p per litre) to heat the house, which as we’ve mentioned many times, wasn’t economically viable. When the air source heat pump went in, we were paying 14p/kWh of electricity, which made it cheaper to run than oil.

But let’s take a look at the January numbers for our heat pump. January had a lot of really icy days and it’s been the longest sustained bout of cold weather we’ve experienced since moving in. Last month, we consumed 2,231 kWh of electricity, just for the air source heat pump, which is a crazy amount at around 72kWh per day.

Over January, we were lucky in that our Symbio rate was still 11p/kWh. That expires at the end of February, and we can’t find a provider for anything less than 16p/kWh. We don’t have a smart metre, so we are reliant on competitive set tariffs. Having said that, most people on smart metres with agile tariffs are averaging around the 15p/kWh mark in January.

So what does this mean? To answer that, let’s put our January consumption into the table below and see what it costs to heat our house based on these various rates during a cold month.

Tariff Cost on 2,231 kWh consumption

I find the numbers above a tad scary. Yes, we’ve had a cold January, and February so far is equally icy with beast from the east blizzards, and as climate change continues to throw up colder winters, I’m not sure how economically viable it’s going to be to heat this house if electricity rates don’t drop.

As mentioned, we’re super lucky that we have a low tariff for January and February, but that’s not going to last, and at that rate we were able to heat this house at £245, £5 less than what we were paying for oil.

It looks like the best tariff we’ll be able to get for 2021 is 15p/kWh and that shoots our heating bill up to £334 on January’s consumption, which is mad, and it isn’t financially viable in the long-term. I suppose we’re getting some assistance from our solar PV, and in January we generated a modest 161kWh of power. Since we’re on a tariff of 11p/kWh, we’ll apply the same value, which means we can shave off £18 off our January heating bill.

So it’s an issue for us going forward, and the issue will apply to all people with an air source heat pump, irrespective of their home size and what they’re paying for heating because it’s all relative. Everyone’s bills will get higher with more consumption and higher rates.

So I think the UK government has a problem on its hands. They are driving the market for more and more people to switch to ASHPs, but they will become unaffordable to run. Unlike gas or oil, you can’t just switch the pump off to save on heating and then turn back in when you get too cold, because theses pumps can take days to reheat cold rooms and that reheating process is incredibly inefficient.

I can’t see a feasible, sustainable, financially viable way of running an air source heat pump at tariffs over 15p/kWh and that, for the first time, has me worried. I spent the weekend on comparison websites and visiting providers directly. Most tariffs are at 16-18p/kWh and that’s going to be extremely expensive if we start to have regularly cold winters.


Simon Kovach 8 February 2021 - 22:03

Thanks for your posts, I’m a new subscriber and your previous articles on ASHP are/were swaying me towards one over oil (we currently have a thermal store and logburners). That is now starting to look prohibitively expensive to me which is very disappointing….thank you for you honest post though. Your website and YouTube channel are excellent though and inspirational, keep it up!

Mars 8 February 2021 - 22:57

Thanks for the feedback Simon, and the nice comments. Glad you’re enjoying our posts and videos.

I’ve just replied to Julian with thoughts on running costs and oil. It’s a tough one. If electricity isn’t pulled back for ASHP users, it’s going to get prohibitively expensive to run in winter months. There’s a lot to think about, and I need figure out a sensible heating strategy before next winter. It might involve jumping from ASHP to oil, which obviously affects our sustainability drive. There’s a lot to think about.

Do you presently have an oil boiler?

Simon Kovach 9 February 2021 - 06:16

Hi Mars,

No – we literally have just a thermal store and two log burners linked to UFH. It was installed by the previous owner and doesn’t work, I saw, split and burn 12 tonnes of wood a year, which only covers my hot water for winter. During summer we use immersion heaters for hot water. It’s a huge amount of work to keep on top of the wood and is massively inefficient at best. I may just go for an oil burner for now to avoid another winter having to set fires like a caveman!

Mars 11 February 2021 - 16:20

Nothing wrong with a solid caveman fire!

jeanette winterson 28 June 2021 - 16:38

hi there – my air source is costing me around 6k a year to run – yes you read that right – and I have solar PV and a well insulated home. I am going to pull out soon and go back to LPG

Mars 29 June 2021 - 08:23

Thanks for the comment Jeanette. £6,000 is a staggering amount, and we’d love to find out more as to why this figure is so high. I would like to invite you to join our growing community on Renewable Heating Hub, and would appreciate it if you could sign up and participate in our forum discussions and share your experience with many homeowners across the UK: https://renewableheatinghub.co.uk/forums

Schmitt Trading Ltd 29 June 2021 - 21:10

Hi Jeanette,
I would also be interested in what you are planning to do.
Run a Stirling motor with LPG?
This is also my consideration…

Barbara Vincent 4 September 2021 - 19:55

Omg! Really? We have just one fitted. I am so disheartened.

Mars 5 September 2021 - 07:31

Don’t be Barbara. Which pump have you installed? The price of electricity this winter is going to the real issue. What’s your tariff and who is your provider?

Barbara Vincent 5 September 2021 - 21:11

Have a 6kw Mitsubishi with a grant tank. Haven’t got a tarrif yet but Octopus Go looked good. Don’t really know if there is any other company that does a tarrif for ashp. Not much help from company that sold it to me or the installers.

Mars 5 September 2021 - 21:35

I think your heat pump will keep you in good stead. As for the tariff, you don’t need an ASHP tariff. You just need any provider with the lowest tariff rate, so shop around. If you have a smart metre, you may be able to utilise off peak rates to your benefit.

Neville Walker 5 December 2021 - 03:44

Hello Jeanette

I too am facing bills of that magnitude for a four bedroom house that I recently moved to. It’s crazy – in my previous, older and only slightly smaller house but with a conventional combi boiler my power bills were a quarter of what I’m now facing.

And the worst of it is that half the house is so cold it is barely inhabitable in the winter. I’m very disillusioned by the whole experience.

Thimbles 5 December 2021 - 09:38

Hard to understand these figures. I am having an ASHP installed next week having checked out all the heat calculations and financial costs in some detail which is easy for me as I’m a Chemical Engineer. In short for a 4 bed old farmhouse my domestic electricity consumption is 8,000KWH/year. Until this month this cost me £100/month average at £0.14/KWH. My supplier has gone bust so I am now transferred to BG at £0.21/KWH i.e a 50% rise to £150/month. My oil system uses about 2,200L/year (about 20,000KW) at £0.6/L which is £110/month average. The ASHP will deliver the same heat load at COP of around 3 meaning it will use about 7,000KWH/year costing about £120/month at the new higher rate. i.e £10/month more than oil. Obviously with a new forecast total consumption of around 15,000 KWh/year (£ 260/month) I will shop around for a better electricity deal as soon as possible but I don’t see how costs can ever exceed maybe £300/month for a 4 bed house unless the ASHP system is completly mis-configured and is running at hopeless efficiencies?

Jennifer Ross 9 December 2021 - 20:59

Thimbles – I don’t understand those figures either. We have a 4 bedroom house and had an ASHP installed in September 2021. Our heat pump is a 12kW Vaillant.
The cost of heating and hot water from 7 November – 7 December 2021 was £144. The heating is on from 06:00 hours to 20:30 with a 2 hour break in the middle. The hot water is set on for a 12 hour period.
We live in a frost hollow in eastern Scotland and have gone through two storms in the last two weeks and overnight temperatures hovering at around zero for the last fortnight.
Our home is timber-framed and reasonably well insulated but the bedrooms upstairs have 30 years old velux windows which are not particularly well insulated. We only upsized the downstairs radiators. Despite all of this we find we are warm and cosy.
We have used our wood burner twice in the last month. We are with Octopus Go and are currently on a low rate of £0.13/kWh. We had anticipated winter energy costs of up to £300 per month and of course that might happen if our tariff doubles. However, for us, our overall costs are considerably less than we used to pay with electric boilers and our £100/month wood fuel consumption has fallen significantly. At £300 a month for 6 winter months and £100 for 6 spring/summer months our overall annual cost would be under £2,500.

Barbara Vincent 9 December 2021 - 21:54

Octopus Go is now 24p kw/h! Don’t know what the best tarrif to go on now?
Does your system work alright if you put the heating and water on a timer?

Thimbles 10 December 2021 - 18:49

I’m pleased to hear your experience chimes in with the calculations I’ve made for our house. I’ve been up and running 3 days now with typical December temperatures of 3 to 6C here but already I can see the power consumption is slightly less than I was expecting so no surprises. I’m still tweaking the schedule to get the temperatures I want at each part of the day but almost there now, it has been surprisingly easy. I was planning to generate hot water just once per day in the warmest past of the day but was advised to leave it as an “on demand” schedule for now, i.e it makes hot water anytime it senses it needs to top up, so there may still be further improvements to come. My installer, who is excellent, provides a ” full service” meaning he provides ongoing system optimisation (he has access to the controls via the internet on new systems) plus regular electricity supplier advice. Current advice is to sit tight with my replacement supplier until the Spring as there are no good deals out there that will significantly save on the capped price. Hopefully the supply side will settle down soon and new deals will start to appear.

Kelly 18 September 2021 - 23:12

Well I live in affordable housing, so I rent from a housing association. I have an above ground heat pump. Currently running through 11500kwh a year. Paying around 245 per month. It hurts and its totally ineffective.

Barbara Vincent 19 September 2021 - 08:29

That’s terrible! What tariff are you on?

Jenny Ross 19 September 2021 - 15:01

Hi Kelly

I don’t understand why your monthly cost is so high. We are currently on a tariff of 13.5p/kWh (and 5p/kwH for 4 hours overnight). On our tariff you would have averaged £129 per month. Usually of course you would spend much more during the winter than the summer. Our August 2021 cost was £40 without any radiator heating.
Previously, over the last 5 years on electric boilers we averaged 12,000 kWh per year and, for at least 9 months of the year, paid significantly less per month than you are paying. Electric boilers are well known to be substantially less efficient and markedly more expensive than the cost of running an ASHP. It sounds to me as though you are either on the wrong tariff or your ASHP has been wrongly installed – or perhaps both.
Are there other tenants in a similar position who are experiencing the same costs as you? Are you able to change electricity supplier or is the Housing Association responsible for this? It would be worth finding out and, if so, submitting a joint or communal request to your Housing Association to ask them to change to a cheaper supplier and to arrange for an expert opinion on whether your ASHP is actually installed correctly. Failing all that go to Citizens Advice.

Barbara Vincent 19 September 2021 - 18:27

What company are you with, please, to get a tarrif that cheap?

Jenny Ross 19 September 2021 - 19:03

Barbara – we are with Octopus Go

This was our most recent invoice:

Breakdown by rate
Rate Consumption Cost
4.76p/kWh 80.4 kWh £3.829
13.51p/kWh 232.3 kWh £31.381


Barbara Vincent 19 September 2021 - 19:31

That’s the tarrif I am in the process of changing to but I think it’s 15p a unit. Just transferring to octopus energy.

Jeni Parker 10 January 2022 - 13:22

Hi There, I’ve just moved into a bungalow with an ASHP & my electric bill was £324 for 5 weeks. KWh from Octopus is 23p…Gas boiler in old house was cheaper & more efficient…loft is well insulated & its on 19 degrees, 6.30am – 9pm. Got solar PV panels too..awaiting Fit payments each quarter.

Julian C 8 February 2021 - 22:34

Hi. When you home was MCS assessed, what was the electric consumption prediction against what parameters? I recognise the concerns in your note about electric prices.
I’ve written elsewhere I’m investigating an ASHP to replace my oil boiler. My prediction is 7344kWh annually at a SCOP of 3.64 giving 22672kWh of thermal heat. This at -3.4C. With water temp at 45-48C. This feels reasonable as we currently use 1200-1500L of oil per year. 1L = 10kWh of energy equivalent.
Appreciate your thoughts

Mars 8 February 2021 - 22:52

Our calculations were based on about 11,500kWh annually, which at 14p/kWh made sense.

Your numbers stack up nicely, but the thing where everything hinges, for us, is the price of energy. Oil is currently around 30p/litre (I think) which makes it quite cheap to run a central heating system, When it hits 50p, which it will again at some stage, that bring it line, for our property, to electricity at 14p/kWh. My concern is what happens when electricity keeps rising, which is a high probability, and we can’t get it at less than 17-18p. What then? Do we fall back on our oil boiler and start chugging the diesel, because it gets too expensive to heat the house in Dec/Jan? And that’ll affect RHI payments. It’s a tricky one, and we need to find a solution before next winter.

As an observation, we run our hot water at 42C and it’s hot enough. Anything over 45C, and you’re using cold water to offset it because it’s too hot.

Julian C 8 February 2021 - 23:19

I appreciate all the points you make. I think paid about 19p/L last June for 1500L of oil. But it’s up to 35p/L now. I haven’t jumped to ASHP like you yet. So I’m still comparing the estimates to likely actual. But oil prices will keep rising. If we get of fossil fuel electric generation, then prices stabilise. But your economic view is still correct. Hmmm difficult

Mars 9 February 2021 - 07:50

Oil has always been volatile. I would imagine it will rise, but given that the world will continue to stay in lockdown into next year (at least), I don’t see it going over 40p in 2021. But you never know. Electricity is more stable in terms of pricing, which is worrying in its own respect, because once it hits a price point, it won’t go below that.

Mark+Crooks 9 February 2021 - 06:55

Yes somewhat concerning on the face of it, especially as I’m still in the throws of having my ASHP fitted and just had the LPG tank uplifted and removed 😳.

But we have to consider that all energy will become more expensive. Yes oil is cheap at the moment but it most probably won’t stay like that. I received an email from my LPG supplier that it was raising the cost by 6ppl with immediate effect, that’s a 15% increase in one hit.

Hopefully with information hubs like your website, ASHP users can share tips on efficiency settings they have found to be beneficial which might help chip away at running costs.

I’m a little confused about your figures. You say that you spent £250pm on oil. Is that based on averaging out £3k per year? Personally I think it’s important to work with annual figures when comparing costs.

And also let’s not forget as you have previously mentioned that you’re getting heating 24/7 now rather than partial heating with oil, so the comparison isn’t like for like.

Mars 9 February 2021 - 07:55

Agreed. All fuels will go up. Surprised by the huge LPG increase though. Wonder what was behind that.

As for our oil consumption. We were paying just over £2,000 a year, when oil was selling between 45p-55p per litre. And yes, our heating now runs 24/7 as opposed to intermittently on oil, and the whole house is heating as opposed to pockets when running oil.

Figuring out how to economise is going to be the challenge.

Ron 9 February 2021 - 08:04

A way to save costs in wintertime could be to pocket a few less used rooms in the house and (if they are zoned) set them at a lower temperature on the thermostat?

Mars 9 February 2021 - 08:14

We did that last year Ron. We have smart TRVs on our rads, so we set lower temperatures in different parts of the house at different times of the day and consumption was the same as the whole house being on this winter. And it makes sense, because if the pump’s on, it’s heating water for the central heating, and it’s affected by the ambient temperature at the time. So if any part of the house is calling for heat, the pump will be heating water, consuming electricity based on the outdoor temperature. Lower room temperatures don’t work in dropping consumption, in our experience, in our case because the pump is still heating flow rate temperatures to 45C irrespective.

Ron 9 February 2021 - 07:46

Our 11 kW ASHP used 1,120 kWh in January. I think our reasonable consumption is a lot to do with the insulation and the airtightness of the house. Especially the latter makes a big difference I feel. Is airtightness something you could improve on Mars?

Mars 9 February 2021 - 08:01

We worked a lot on insulation and airtightness last summer, and it’s made a big difference to the way the house retains heat this winter. We will do more again this summer.

The thing is, our pump still has to run 24/7 because keeping rooms to temperature is a 24/7 exercise, and that’s not going to change our consumption, hence my apprehension about rising tariffs.

Might batteries and low overnight tariffs be the way forward to cut chunks of our expenditure. Maybe. But it’s a heavy investment with something like a Powerwall. Will have to do some number crunching.

Ron 9 February 2021 - 08:08

I have been thinking about lower off peak tariffs as well. It would make sense because at night the temperature outside drops and the ASHP has to work harder. At that same time the heating demand in the house is higher than in the daytime as well. I would have to get our meter exchanged though, because at the moment we have a standard rate meter. Wonder if they do 3-phase off peak meters…

anna+mycoe 9 February 2021 - 08:20

Hi Mars
Your concern is shared somewhat at this end, I’ve run up a bill of £300 for the first month of use. And it’s not that warm indoors without the wood burner we would be cold. They function great when the ambient air temp is around 2-4 degrees. We are looking at a wind turbine as an option, as this will run in the dark and generate 24/7 when it’s turning, so we can have the HP on all the time in the winter. Not 100% convinced we have made a good decision on this heat choice, an oil combi would have been circa 6k. This system cost me 12k, without the RHI the ASHP simply isn’t viable financially for most. Wind will cost in the region of 7k if we go for batteries
Needs some serious thinking about by someone smarter than me in Whitehall !

Jenny Ross 9 February 2021 - 10:10

Hi Anna – when you say the temperature inside your house is not ‘that warm’ could you let us know what sort of temperature you have inside with the ASHP? We are currently surviving this winter in a rural area in the east of Scotland (one of the coldest winters we can remember with temperatures around 1 deg C since the end of November) where our house temperature is consistently around 12-13 deg C. This is because we can only afford to have our electric heating on for about 3 hours a day and that costs us about £280 a month over the winter. We are considering an ASHP because we reckon that nothing can be as inefficient as our current electric wet heating system. We would be happy with 17-18 degrees inside…..

anna+mycoe 13 February 2021 - 10:31

Hi Jenny
The temperature we are achieving is around 18!when it’s been – 3 outside. We live in the Pennine hills at the Sheffield side, very exposed so maybe comparable for you. It’s not freezing by any means, it’s just it takes an absolute age to get up to temperature so we too have decided to leave it on 20 degrees. 24:7 and see what happens to the cost.
Ours is also retro fitted to the existing circulation pipes with upgraded Rads so we may need to look at re piping the system in the summer. I’m a gas engineer by trade so not an issue for me if needs be
Hope this helps

Mars 13 February 2021 - 13:44

Our house is also struggling at the moment – we’re running at about 19.5-20C in most areas where we typically manage 21-22C with outdoor temperatures at 3-5C. Also doing about 95kWh in electricity on a daily basis, just for the ASHP. Ouch!

Jenny Ross 13 February 2021 - 16:52

Thank you Mars and Anna/Mycoe, I have found all the conversation threads just so very helpful and very interesting. Thank you Mars for your brilliant videos and for keeping the debate going. We would be absolutely delighted to have room temperatures of 18 degrees. The wood burner in our living room keeps us alive during the winter months. We have had a few nights in the past month at minus 15 degrees. We will definitely consider an ASHP as we manage to get through about 11700 KwH annually having only an electric pump to heat radiators and water.
During the last 3 months our hall and downstairs bedroom (which we sleep in) temperature stand at about 9-13 degrees when the heating is off, which is for most of the day. So we consume a significant amount of energy and the house is cold.
Having had snow lying for the last 10 days has allowed us to see whether our roof insulation is working (it is). We don’t know how to work out whether or not we have cavity wall insulation but I suspect not. The amount of snow we have had has also encouraged us to consider ASHPs where the fan sits higher on the pump itself.
No one has yet mentioned wearing more clothing – but that’s what we do too – and it works!!
Thanks again.
Jenny and Jim

Mars 14 February 2021 - 08:24

I have to say that you guys would push ASHP limits by UK standards. ASHP consumption will be incredibly high at -15C, but it should still heat the house. The snow is an excellent point too, and you’d need a high evaporator or install the pump at an elevated level if you get a lot of settling snow.

Insulation. The million pound question. We did some forced DIY work as a result of a leak (which lead to a new master bathroom) and we discovered cavity insulation in stud walls facing the exterior brick, but nothing in the interior stud walls.

We’ve also mounted some heavy artwork using industrial strength plugs that we had to drill in, and also saw insulation in other rooms. No idea how thick though.

Wearing additional layers, at your current temperatures, would not be a bad idea 😃

Mars 9 February 2021 - 10:14

We share your experience to some degree – we’re able to maintain most of the house (apart from the TV room and downstairs guest bedroom) at 21C, but you can definitely feel an ambient change in the air around you, and that occurs when temperatures drop below 3C. So the fires really help to take that chill from the air. They’re super important to us too. I’m still intrigued by your wind proposition and am really keen to see how that goes.

As for Whitehall, I think you’re giving them far too much credit.

anna+mycoe 14 February 2021 - 18:29

Hi all
Just an update on the temperature in the house.
We have a 300 year old cottage with a modern (looks old) extension and a conservatory. We bought the house just over 18 months ago, and inherited an old oil guzzling combi. Hot, but hated !
The air source has been in a month now, and we are getting used to it finally. This week it has been -3 most nights so I took the plunge and have just left the HP on 24/7 about 10 days ago. The house has been noticeably warmer and more comfortable.
The insulation in the property is crap, with only loft insulation, the downstairs is a concrete slab laid probably mid 80s so basically a giant heat sink. So in reality an ASHP was probably not the smartest move. However! We are now ticking along at about 20 degrees, so comfortable, with the wood burner on its lovely and we leave the door open so it trackes through the house. Our conservatory is like a leaky sieve, so we have turned the rads right down in there. It will be coming down in the summer and being converted to a proper room so then it will be fine, and that room too will have a wood burner, so both ends of the downstairs will have wood fires. The rest of the house I have let the rads stay on3-4 so it ticks over at a reasonable temperature, and I can’t stand a hot bedroom anyway. The bath room is a little cool, but it’s an old fashioned towel rad, fully tiled ceramic box with two outside walls, so thermal loss is ridiculous, that will get solved when we rip the terracotta 80s monstrosity out. I’ll insulate.
I’ve tracked the ASHP electric usage for a couple of weeks. Ours is a largish 3 bed cottage, double glazed but no other really energy saving measures.
Meter readings
1st Feb – 21636
13th – 22461
Usage 825Kwh
Our electricity is 12.8p per KW he (igloo energy pioneer tarrif, cheapest I’ve found)
If my workings are accurate then that’s
£105.60 for two weeks, on constant.

Oil was similar, but it wasn’t on in the night, plus we had the monster in the kitchen, noisey and hot.
Plus we had an ugly oil tank which has now gone to create room for a workshop. So at this point, im optimistic that it may be a decent investment with the RHI


Jenny Ross 14 February 2021 - 20:11

Hi Anna
Thanks for the update.
One other question – what make of ASHP did you opt for and what size was it? We have been recommended an 18Kwh Caernarvon heat pump, which seems quite large for our 3/4 bed cottage style property.

Mars 14 February 2021 - 22:04

Very insightful and helpful Anna. Thanks for sharing.

Our conservatory is a horror story to heat too. It’s a battle we can’t (and won’t) win.

Thanks again for sharing.

Antony Flynn 27 June 2021 - 17:13

People talk about the ashp outside being very quiet, but what about the hot water tank and associated pipe work in the cupboard in the house ? Is there and noise from it? I only ask because the hot water tank is due to be fitted in my house in the old airing cupboard next to the head of my bed and I dont want to hear it making noises all night

Mars 29 June 2021 - 08:30

Hi Anthony. If you have your hot water tank the room already, then there shouldn’t be any more additional noise than what’s there already. We recently upgraded our internal distribution pump in our house, and it’s a bit noisier.

On a related note, I would like to invite you to join our growing community at Renewable Heating Hub, and would appreciate it if you could sign up and participate in our forum discussions where you can ask this question and get feedback from other homeowners: https://renewableheatinghub.co.uk/forums

Barbara VINCENT 8 November 2021 - 20:43

Good luck getting any sleep. Ours rumbles a lot at night and is almost below our bedroom. Quieter in the summer obviously as it doesn’t have to run the heating.

Julian C 9 February 2021 - 08:48

I wonder what else I could do for air tightness? I’ve replaced open extraction fans in bathrooms with ones that close. I’ve covered up key holes. We have 50mm of cavity wall insulation in a 100mm cavity. Should I get that filled? Else we have 300mm loft insulation and triple glazing. Front door looks nice, but isn’t well insulated or sealed.

Mars 9 February 2021 - 10:16

Wow. You’re covered from an insulation perspective. The triple glazing is especially awesome. We have double glazing, and I want to look into those clear films you apply to windows that trap radiant heat. Anyone have experience with those?

Steffan 9 February 2021 - 11:33

Hi Mars,

I feel your frustration. My house is fine, but my home office is in a conservatory and with all that glass it’s cold this Winter. It’s uncomfortable without a heater on all the time but that costs extra money on top of heating the house seperately so I don’t like doing it.

(For both of us) this problem is not going away as electric is going to get more expensive over time and so doing more with less is the only strategy.

Some ideas.
Double to triple glazing the difference is only small in the UK climate (of course if you live in Scandanavia then it’s different). An extra plastic film likewise won’t help you that much. You are better off making sure the frames and seals of windows are clean. Trapped dirt can sometimes pry open leaks for cold air to come in. Make sure they are no gaps in the frames and you can’t see outside light coming in from any angle when the window is shut. You cant adjust windows (usually) so you will need to put some insultation strip to cover any gaps.
Same thing with your front door, make sure it closes tight and is clean. A modern door is adjustable so you can adjust for a tight fit. I sometimes have to adjust my doors slightly summer and winter, because of expansion and contraction with temperature changes.

If you have solid walls then putting tin foil behind radiators can avoid the radiative heat going into the wall. There are professional products out there that would help in your case (of solid walls) but tin foil on cardboard is the DIY version.

Carpets and rugs. Did I say that I think that 50% of my house heat loss is to my solid concrete floors? (Bungalow with uninsulated concrete slab and vinyl flooring – looks nice but it’s a giant cold stone). If only for the Winter more floor coverage is better.

Setting back the temperature in hardly used rooms will save you energy. Close the door and let the room go cold. It will take a while for you to notice the saving as you have solid walls. Spare a quick thought for damp, get a humidity sensor and if you are reasonably airtight get a dessicant dehumidifier (better at low temps).

Think about not running your heat pump overnight. I don’t know your particular set-up however the air is coldest in the middle of the night and hence the heat pump is at its least efficient in producing heat. Turning it off overnight and working it harder midday to get the heat into your house makes more sense (and will save you some electric on de-icing cycles). If it’s too cold in the evening then overheat your house during the afternoon to tie you over through the evening.

External walls that are always in shade and people won’t see them, then think about some insulation. You could go for proper external wall insulation however I would be tempted by some DIY wood cladding or even some bushes or shrubbery (anything to partially shield the wall from surrounding air flow).

Just a note: I am a professional in this field but I don’t guarantee any of these ideas will work.

Keep at it, there are dozens of small things you can do to keep in the warm. Don’t go back to the oil boiler, that would be a set back.

Mars 9 February 2021 - 21:34

Another outstanding reply Stefan with some terrific ideas. We’re definitely going to look into them this summer. The foil behind the rads is a good one. There’s so much to do.

Fully onboard with the fans – they drive costs up and only heat tiny areas. Some nights, like tonight, needs a fan in the TV room, and the fires have been on since since after lunch to keep the main living area warm.

Mars 9 February 2021 - 21:39

As a separate question Steffan, today’s been the coldest day we’ve ever had since running an ASHP (-4C). Our master bedroom rads are always the hottest (with a 45C flow), but tonight they feel very warm (and not hot all). I’m perplexed at how this occurs when temperatures drop. Hot water coming into the house at 45C and leaving at 40C. Is there a reason you can think of.

Steffan 10 February 2021 - 10:14

I would think that the 45C water coming into your house from the heat pump is being partially cooled before it reaches your master bedroom radiator. This might have two causes:

(1) The water reaching your rad its being cooled before it gets to your rad. This might mean your house internals are that bit colder. If for instance the water is circulated through your roof space then the cold air in the roof is colder so it cools the flow faster than normal. llikewise, if the flow is going through internal cavities or the floor then the floor is that bit colder etc
(2) The flow speed of the heating circuit may have slowed down. A potentially compounding problem with (1) , in order to maintain 45C output flow at the heat pump when the air is so cold, the heat pump reduces the flow speed of the heating circuit. Less flow means less heat energy per second going into the rad. (and also more dwell time in the colder parts of the house). A heat pump in theory shouldn’t do this, instead it should use direct electric heating to make up any shortfall in heat from the air and keep the flow speed the same. However, programmers may have in practice reduced the flow a little bit in order to reduce the amount of direct electric heating. You could ask the manufacturer.

p.s., Your hands are never a reliable guide to temperature, because your internal body temperature and blood flow to skin varies so much (you need a sensor – even a dangly outdoor garden sensor taped to a rad is good enough).

Mars 10 February 2021 - 14:26

Your assessment is sound and makes sense Steffan, and both points 1 and 2 may apply to us. Our piping to the rooms upstairs runs through the stud wall, and has (apparently) been insulated. One of the walls we broke into last year to fix a leak showed that our central heating pipes were insulated. But I wouldn’t put money on it being the case throughout the house.

I will raise point 2 with the manufacturer and see what they say.

Derek Marsh 22 February 2021 - 12:38

Hi Steffan& Mars,
As Mars is aware, at the moment I am collecting data and knowledge concerning ASHP and their operation to decide if they are a viable alternative to our present old gas boiler.
As you described in (1) there may be a slight loss of heat energy within the pipework of a central heating system, but this should be fairly minimal if the pipework is adequately insulated.
I was more intrigued by your comment about the change in flow rate in (2). Do you know this to be a fact?
My understanding of central heating water pumps, is that they run at a fixed speed and hence reasonably constant flow rate, unless additional equipment has been installed such as a diverter valve, pressure relief/bypass valve or motor speed controller. Do you know if any of these are used with ASHP’s?
In my particular central heating system the pump and boiler are switched on and off by the temperature controller, which I have installed to replace the thermostat. The system is designed to vary the temperature of the radiators to replace the heat losses and hence maintain a constant room temperature.
It does this by switching the pump and boiler on and off more frequently than would be the case with a normal thermostat. The end result is that the temperature of the radiators is varied as the outside air temperature varies. At an outside air temperature of 10C, the radiator temperature would be in the range 32C to 34C. Recently the outside air temperature fell to -4.5C, which necessitated a radiator temperature of 42.5C to maintain an indoor temperature of 20C.
It would appear that in the system that Mars has fitted, the water flow temperature from the ASHP is set at 45C, so that the temperature control in the rooms with radiators fitted is performed by the TRV’s. As the heat losses increase, the TRV’s will open more to allow a greater flow, and hence more heat energy into the associated radiators and therefore maintain the desired temperature within the room. If the outside temperature falls sufficiently, there will be a point where the TRV is fully open, and the system may no longer be able to maintain the room temperature. The only way to restore balance would therefore be by increasing the water flow temperature from the ASHP.
A question for all of you with ASHP’s, do you know or have you noticed that the flow and return water temperatures from and to your ASHP vary with climatic conditions or are they fixed?

Sue Laverack 9 February 2021 - 12:12

I am not sure how oil and gas costs have changed in the last few years but it may be that whatever system you have the costs have escalated. I have an ASHP which replaced a solid fuel range which provided heating, hot water and cooking. The original idea had been to source most of our fuel needs from our own woodland but as my husband’s health deteriorated we found ourselves buying more and more coal to supplement what we could grow and cut; coal which was dirty, hard work, bad for the environment and expensive. If I was younger and had enough land I would go back to a wood fired system. As it is I am 70 and although fit enough at present to fell trees and cut firewood I am not sure I could do enough for all my needs, nor how long I could continue to do so.

Mars 9 February 2021 - 21:43

Thanks for the feedback Sue. Energy prices will all be increasing, but I feel electricity won’t go down after it hits a certain point. Are you guys satisfied with the tariff you have and have you found that the pump is keeping you warm this chilly winter?

Neil B 9 February 2021 - 18:37

Hi Mars, thank you for the interesting post.

We have an ASHP, just under a year old, and we are on track to use 7000kWh for the full year. We have just switched to Octopus, the Go Faster tariff I chose has 4 hours at 5p/kWh from 02:30 to 06:30 and 13.31p/kWh for the other 20 hours. I now run the heat pump from 03:00 to 21:00, so at least we are getting 3 and a half hours at the cheaper rate. The net cost therefore becomes a little under 12p/kWh which at least is somewhat better.

Our house is about 100 years old and solid wall, there’s no cavity so it is really cold. The 11kW heat pump we have only just copes at keeping the temp at 21C in the main rooms; bedrooms and hallway a bit lower of course. I have decided that no way do we want to go back to oil, so the best way forward to improve our comfort and reduce costs is external insulation. It is pricey but at least we will get £5k off from the Green Homes Grant.And it will improve the external appearance with a nice clean rendered look. Good luck.

Mars 9 February 2021 - 21:47

Super interesting Neil. Thanks for posting. Maybe a smart metre is the way to go. The 13.31p is very decent. I would snap that up if we had a smart metre.

It’s also impressive that you’re keeping the house at 21C with no insulation.

We really don’t want to go back to oil, and I’m sure we’ll figure something out.

anna+mycoe 14 February 2021 - 18:50

Hi Mars
What don’t you request a smart meter from your supplier? I’m pretty sure they should just fit you one

Mars 14 February 2021 - 19:48

We weren’t in a coverage area last year. We will look into it this year.

Ron 10 February 2021 - 09:51

On https://clubs.moneysavingexpert.com/cheapenergyclub you can find a Symbio tariff of 13.2049092p per kWh (Low Fair and Green 12M Fixed SE01 v18). Is that any help for you Mars? There is also a 18 months fixed for 13.293798p per kWh.

How is your experience with Symbio? There are quite some bad reviews on the web…

Mars 10 February 2021 - 09:57

I have emailed Symbio requesting a longer term deal for the rate cited and they have not replied. It’s been 4-5 days since my enquiry, which may answer your question about their customer service. And yes, we would be happy to lock that rate in. I’ll keep you posted on our Symbio experience.

Julian C 10 February 2021 - 10:02

Love it when they carry so many decimal places 😂

Mars 10 February 2021 - 21:14

Yeah 😂 Talk about precision.

Bob Bazley 14 February 2021 - 13:59

with 6 decimal places would it really make that much difference from just 2 decimal points ? especially when you can only charge people to the nearest penny ?

Mars 14 February 2021 - 21:52


Steffan 10 February 2021 - 10:19

For those of you who like number crunching heat-pumps.

Trystan has achieved some really high COP, however has made some compromises to do so. You might be interested in the pros and cons of those compromises.

Mars 10 February 2021 - 14:22

Wow. That’s pretty detailed. Will need some time to digest that.

Ron 10 February 2021 - 18:37

I’ve had a detailed look into his figures and to be honest I find it really hard to believe he only used about 320 kWh in December 2020 for combined use of his heatpump. Am I missing something?

Derek Marsh 10 February 2021 - 22:37

Hi Everyone,

I have been reading with interest the various comments surrounding ASHP and energy costs etc.
At the moment we have an old gas boiler for both Central Heating and Hot Water with a hot water tank with immersion heater. Because we also have solar panels I have been looking into replacing the gas boiler with an ASHP.

Being a Yorkshireman (we have short arms and deep pockets) I don’t mind paying for things provided I get good value for money.
Having worked for many years in the Power Industry, both in the UK and abroad, on numerous projects fueled by Coal, Oil, Gas, Household Waste, Biomass and Nuclear, I think that I can confirm that your fears about energy prices are correct, in that they will only go in one direction over time. Part of my tasks in designing and optimising control systems was to provide the most efficient system possible within cost constraints. But there comes a point where it is no longer cost effective to make further improvements.

From the point of view of home heating systems, the vast majority are controlled using thermostats, which are not ideal in that they are an on-off device and hence cannot give accurate temperature control. Personal tests have shown that the human body can feel the effect of a 0.5C change in temperature. The better modern thermostats have a switching deadband of 0.5C i.e. the heating is switched on when the temperature falls to say 20C and then is switched off when the temperature rises to 20.5C, which can actually lead to a variation in room temperature in excess of 1C.
I have designed my own control system at home which keeps the temperature at the desired setpoint within plus or minus 0.1C, thereby reducing the need to keep the thermostat set higher than is necessary to be comfortable during the lower temperature swing caused by a thermostat.

Heating a home is like keeping a level of water in a bucket in which there are pin holes. To keep the level constant you need to keep adding water to make up for the leakage. This is what your heating system is doing to keep the temperature in your home constant. If you place the bucket into a vessel containing water, the level of which you can vary, the smaller the difference in the level of water inside the bucket to that outside the bucket then the less leakage will occur and hence the less water you will need to add. If the water level outside the bucket (representing the outside air temperature) is equal to the water level inside the bucket then it will not be necessary to add any water.
Since it is not possible to control the outside air temperature, to reduce your energy usage it is necessary to either lower your thermostat or (plug some of the holes) improve insulation.
A good starting point would be to get access to a thermal camera and survey your property to see where it may be necessary to improve insulation. I was fortunate to be able to borrow a thermal camera, but it may be possible to hire one since they are quite expensive.
Insulation is therefore the cheapest and most effective way of reducing your energy consumption and hence costs.
Loft insulation would probably be the easiest and most cost effective followed by cavity wall, which if my memory serves me well has a payback time of approximately 1 year. For those of you with solid walls, my Nephew has put has put insulation on the inner wall surface, which he did himself. I am not certain of the exact cost but I feel it would be cheaper than the external option.
I have also seen kits of plastic sheet (I think similar to clingfilm) which is put on the inner window frame to create a further layer of insulation. This may be a cheap option to try, certainly for the Winter months.
There obviously comes a point where adding more insulation is not cost effective.

As I stated earlier I have solar panels which for obvious reasons produce more energy in the summer rather than the winter when it would be much more useful. I have now had solar panels for just over 10 years and found them to be an excellent investment, since payback was achieved after 7 years.
Early on I noticed that even in Winter there were days when we were exporting energy that we could not use within the house. I researched storage batteries but quickly came to the conclusion that they were not cost effective. I have looked at wind turbines though not in great detail since I would have to convince my wife. (not an easy task).

I had been thinking about ways to utilise some of the excess energy for water heating, the problem being solar is not constant and one could soon finish up importing expensive electricity rather than using much cheaper gas.
Several years ago a work colleague, at the time, recommended a unit I had been contemplating designing and building myself that would divert only the excess electrical energy, but not import any electrical energy. I finished up buying a device from this company called Immersun, which allows the connection of up to 3 individual loads of up to 3kW to be fed using this excess energy. After installing, I initially used the device to provide hot water from Spring through to Autumn, but still found that there were occasions when the water was up to temperature and once again I was exporting the excess energy. I therefore modified the setup to connect to a second load (a 2kW electric heater to provide heat in our home). This was controlled by a thermostat which the Immersun device is design to accept. I can provide more details for anyone who may be interested.

Besides researching ASHP’s I am also devising methods to possibly utilise solar thermal energy, which is much more efficient than Photo Voltaic. More details can be provided.

Sorry for the length of my message, I was trying to cover as many points as possible, though not to the degree I would normally do so. If anyone would like to discuss any aspects further then please get in touch.



Mars 11 February 2021 - 09:16

Thanks for the detailed and highly valuable reply. I agree with what you’ve said on the insulation, and were trying to figure out where to get a thermal imaging gun from. Also love the bucket with holes analogy.

I share a similar sentiment as you about batteries, given that the Powerwall, for example, sells for £8,000.

I have further comments and questions, and will post these later today or tomorrow.

No problem at all by the length of your post – it’s so much helpful information. Thank you for taking the time two write it and share it with us.

Bob Bazley 14 February 2021 - 14:13

Buying pylontech batteries direct and building your own battery system would be quite cost effective. Tesla while good is a tad expensive. Having said that I think any solar array these days if its not matched up with a battery system is wasting potential energy, and using something like octopus go 5p kWh from 1:30 t to 4:00 am over night charge to bring the batteries back up to full power to supply your energy demand during the early morning when solar isn’t producing enough and then to get them fully charged again during the day when solar has excess, means the batteries are giving you power after sunset during the highest cost of electric and they then run down and get charged up again repeating the cycle. I only just have my Solar array and battery setup installed two weeks ago but the results are impressive considering its winter ! having said that adding an ASHP will probably destroy my current good feeling !! haha

Mars 14 February 2021 - 21:55

Spot on. We do not export at all in winter. It all goes to the ASHP. How large are your batteries.

As for Tesla’s Powerwall is more than a tad expensive at £8,000 🙂 That’s more than our PV cost.

I think we will seriously look at a smart metre this year.

Bob Bazley 15 February 2021 - 08:59

Mars, Batteries absolutely are the way forward especially with a smart meter installed and a service like Octopus (I’m not a sales person for them but they right now offer a tariff that is only 5p for overnight charging of your battery/EV). Having said that I need to get a smart meter installed to enjoy those benefits and I have no idea how long that could take ! My battery storage is 4.8kwh(2 x 2.4kwh Aoboet batteries) I think that potentially batteries in their own right might not give you the ROI that you want but when matched with Solar then I believe it increases your value from Solar production. If your exporting Solar to the grid during the day your only getting a small amount of value from it but if you export that power to a battery and then use that battery to supply power when their is no solar and in the evening when the grid power is at its highest price then you absolutely benefit in the value. I intend to add 2 more batteries to give me a total of 9.6kWh which i believe for the vast majority of the time will be sufficient to cover most of my evenings. in the first few weeks of having it installed on good solar days the batteries have been charged fully by the solar within a matter of hours. I’m going to ask my underfloor heating installer and my air source installer for some client names I can speak to in person and get a real feel of what the usage is like especially in the winter time. I haven’t made the final decision yet and its a major investment, it would be so easy to just use the Oil burner and keep the radiators which keep the house warm. If I get the decision wrong i get the feeling it may cost me a lot more than what i currently pay. The fact is that in making these choices you are relying on the professionals that do these installs to be working absolutely in your favour and giving you the best advice about the performance and the costs over time. I often look at green energy improvements as a depreciating asset while it gives me value over time eventually it will need to be upgraded, but then its the same for a new Kitchen, i dont think a lot of people go buying a new kitchen because they think it will pay for itself over X amount of years, they buy it as they want a nice kitchen that suits them and it will add value to the house but then again renewables will do that too. I think you could get a 4.8kWh battery system for around £2500 or less which would make a real difference to your setup.

Julian+C 15 February 2021 - 11:33

Mars and Bob
I would challenge that separate batteries are the answer. I agree batteries are the answer. But I think in EVs with V2G technology. Means you save buying a battery. So for example, I have an Honda e with a 28.5kWh useable battery. It is Vehicle to Grid capable, but the CCS (charge connector) standards have not been confirmed. Chademo (Nissan use this EV connector) trials for V2G are underway. It has to be the better answer than home batteries to balance the grid

Woodlands 13 February 2021 - 11:27

Hi, found a link to your site on another forum. Interesting to read about your experience. We have two small ASHP’s, one in the lounge & another installed in the Kitchen in our bungalow. They tend to keep the rooms at about 20c, even when it is 0c outside. They have reduced our use of gas by over 90%, as the heat filters through to the other rooms.
Someone mentioned the Octopus Go Faster Tariff, we are on the 5 hours from 01:30-06:30 option, paying 5.5p/kWh and just over 14p/kWh for the rest of the time. Our average costs works out at less than 10p/kWh. Also, Octopus have a thermal image camera you can arrange to borrow; so that may help find any poor insulation spots.
Not sure about electricity prices always going up; we are paying less p/kWh now than we did a few years ago.
With more, cheaper renewable generation coming on-line the average wholesale costs appears to have dropped from about £65/MWh to about £45/MWh apart from the “blip” caused by the lockdown in Winter.
In the Spring, Octopus were paying people on Agile to use electricity as there was a surplus.

Mars 13 February 2021 - 13:46

Thanks for sharing. Comments similar to yours are making us think we should get a smart meter installed – hopefully our area will now be covered. Interesting to hear that wholesale prices have dropped, because all electricity providers are spiking and increasing their fixed tariffs.

Woodlands 13 February 2021 - 15:24

Wholesale & Retail prices have peeked this winter because of the lockdown. More people at home using more energy.
The trend, before Covid, can be seen here https://www.nordpoolgroup.com/Market-data1/GB/Auction-prices/UK/monthly/?view=table Especially if you compare 2019 wholesale prices, with those the year before.

Mars 14 February 2021 - 08:05

Very interesting. Let’s see what happens going forward.

Julian C 13 February 2021 - 11:49

Watched your episode 5 ASHP vid. Interesting. Have you considered wearing a wool jumper? 😊. Have you talked to your installers about the 6C change in the home? Why did you choose Grant over other ASHP? Are they the most efficient? Do you have an annual service contract with Grant or your installer? From other YouTube ASHP videos I’ve watched, they suggest different ASHP systems work better/worse in different locations. But then again, I can find NO comparisons between one make and another – not like car test drives. But it is conundrum. Thanks for all your hard work

Eddy Winko 13 February 2021 - 12:21

I remember asking for a quote far an ASHP for a holiday cottage that we are building and they requested a very detailed breakdown of the house insulation before they would offer a quote, it simply isn’t an option over here unless you have followed very tight building codes on insulation and air flow, which for us would have increased the cost of the house considerably. The bottom line for us is don’t go ASHP unless you are well insulated. Of course its a lot colder here and GSHP are more common. Knowing that the water that comes from our borehole at roughly 18c I can see why.
I know I mentioned solar water heating to you in the past as a way of at least taking some of the strain on the ASHP, I was pleased and surprised to see that our water was heated to 35c from the system in bright sunshine despite the the air temperature sitting at -8c all day.

Mars 14 February 2021 - 09:09

Great to hear from you Eddy. Hope you’re keeping well.

We’ve had a lousy winter… little or no sun at all. Solar PV numbers down drastically year-on-year.

Valid points as always Eddy. Are you guys considering GSHP?

Bob Bazley 14 February 2021 - 14:23

Hi Eddy , where is Over here ? UK ? EU, just trying to understand your climate

Mars 14 February 2021 - 21:55

Eddy’s in Polska.

Bob Bazley 15 February 2021 - 09:04

I used to live in Germany not far from the Polish border and i know how cold it gets so going for GSHP might be a wiser choice but much more costly

Mars 15 February 2021 - 09:37

Agreed. More costly and a lot more upheaval, but the RHI payments are much, much higher.

Jon C 13 February 2021 - 18:47

Hi Mars,
Just found your very interesting site, and this post has triggered me to check our usage and costs as I share your concerns. I also think the politicians don’t understand the implcations of banning gas boilers and expecting ASHP to be a suitable replacement.
We live in rural bungalow, extended to be a 330m2 chalet bungalow, well insulated apart from the not very efficient glazed gable.
The old part is heated by a 30 Amp Storage Aga and the new part UFH with a cheap chinese 12kW heat pump ( Model RS-82P5A/T ?) I bought from ebay and installed myself. Water is just an immersion heater.
As our first winter with this the house was too cold, I added a 9kW Electric Assist boiler that the ASHP seems to use quite sparingly. The last two winters have been much better with this, especially after I added a low hysteresis thermostat.
Over the last 12 months we used 6530 kWh day / 10765 kWh night. Which at our current 15p / 7.8p tarrif is just under £2k per year. The cheapest tariff I now see is 18.6p / 9p. So it looks we’ll be paying £350 more next year.
Over the last 5 days we’ve used 158 kWh per day. And the last 30 days, £433 worth of electricity, next year that will be £533. Scary !.
Also interested to see you’ve retained your oil boiler for really cold weather. I’ve seen our usage exceed 80 Amps. The supply fuse is 100 Amps. So we’ll need to replace the Assist boiler with something else (oil ?) if we ever get an electric vehicle.
Hope this is useful.

Mars 14 February 2021 - 08:16

Thanks for the feedback Jon. Your set up sounds interesting, and electricity consumption is a scary thing indeed.

I fully agree with your assessment of politicians; they don’t understand what real world implications this is going to have. If they don’t take appropriate measures, ASHP heating is going to inevitably become prohibitively expensive because electricity demand is going to be too high. The next few years are going to be telling.

Out of curiosity, how are you able to monitor your amp usage?

Jon C 14 February 2021 - 19:02

Thanks Mars, yes interesting times coming up.
I’ve got an OWL USB Monitor that will show AMPs or kWh. I think the voltage is configurable but I’ve not measured and set it, so could be out slightly.

ken B 14 February 2021 - 12:16

So you were using 500L/month of oil (perhaps even more in a comparable month ?) which is 5175 kwh/month before losses.

With the HP used 2231kwh/month and therefore in basic terms you achieved a COP of 5175/2231 = 2.31 which is not bad considering the conditions.

So the basic problem is not the HP or the cost of the leccy but the heat requirement of the house which would seem to need looking into.

I also note that you have 2 wood burners and wonder to what extent you have been using these as these should cater for the heating load by themselves.

Mars 14 February 2021 - 21:50

Thanks Ken. That’s a very interesting way to think about it. Super interesting. We will try to figure out some o& the underlying issues behind why the north side of the house is so much colder and not heating when temperatures drop.

nick 15 February 2021 - 12:12

Depressing reading particularly in the middle of such a cold spell. I have an Mitsubishi ASHP about to installed and don’t want to get cold feet ( literally ) What is the EPC rating of your place ?

Mars 15 February 2021 - 15:31

We’re not trying to discourage anyone from ASHPs Nick. They are the way forward, but it’s a matter of getting the right tariffs and it’s about raising awareness. Our EPC when we purchased the property was 67, with the potential for 76. I think that will have changed now.

nick 15 February 2021 - 15:44

You are evangelists ! FYI i have a Tesla Powerwall for home energy storage and as result I pay a fixed 8p per kilowatt 24/7 to Octopus Energy inc all service charges under their Tesla Tariff.

Mars 15 February 2021 - 19:54

Thanks Nick. So you’re paying 8p 24/7 because you have a Tesla battery and Octopus have a dedicated tariff for Tesla only? Is that right?

nick 15 February 2021 - 19:59
Mars 15 February 2021 - 20:04

That’s amazing. That’s a great plan. Wow. Just need to mull over the £8,000 + installation.

nick 15 February 2021 - 20:42

They ( and Ovo ) also do a plan for V2G – using the battery in a Nissan Leaf for the storage. Octopus will lease you the car over 3 years and throw in a tariff similar to the Tesla plan to further encourage you. Other plans like https://octopus.energy/agile/ are no good for heat pumps due to their pricing inconsistency unless you have got some serious storage.
The powerwall has been excellent – also you can have it set so you can run the house in the event of mains powercut.

Derek Marsh 15 February 2021 - 12:59

Hi Everyone,

We had smart meters (gas and electric) fitted several years ago, I think that it may have been a requirement to get a certain tariff. Whilst the smart meter itself won’t save you any money, it does give insight into how much energy you are using and the relative cost. One thing of which to be aware, is that if you change supplier, your smart meter may no longer function as a smart meter. Not having changed supplier yet I cannot definitively state what the effect would be, I assume that the smart meter would still function as a meter, but the new supplier would no longer be able to read the meter remotely.

I agree with the comments about politicians, who are more likely to be planning towards the next election rather than the future needs of the people, the country and the planet. I suppose in fairness it is not necessarily totally their fault as much as it the fault of the so called ‘experts’ whom they consult. As I have often stated for many years, “I am waiting for an outbreak of common sense, but I am not holding my breath”. I remember reading several years ago where someone had calculated that the amount of energy hitting the Earth from the Sun each second, is enough to supply the energy needs of all the humans on Earth for a full year. We therefore need to get much better at harnessing all this free energy.

Derek Marsh 15 February 2021 - 16:05

Hi Everyone,

Having read some of the previous posts, I am beginning to wonder if there is some confusion between a smart meter and a dual tariff meter.
A smart meter is one installed by your electricity supplier and/or gas supplier which allows them to take readings remotely, so they do not have to send out a meter reader or ask the customer to provide readings.
A dual tariff meter is required when you sign up for a deal where you are charged different prices for your electricity during different periods throughout the day. Normally a day rate which is slightly higher than the single tariff (24hr) rate, with the night rate normally being much cheaper.
I hope I am not ‘teaching my Granny to suck eggs’.

David 17 February 2021 - 09:05 Reply
ken B 18 February 2021 - 08:49

Dual tariff meters no longer exist as that is the purpose of the smart meter to apportion. On some tariffs the rate changes every 1/2hr and all taken care of by the smart meter/computers.

Suggest the north face of your house was the coldest because the wind was from that direction. The air pressure on the north face makes the air in the house migrate from north to south through the air leaks. You also have the effect of wind chill factor on the north face but this can be helped by planting trees,hedge etc on that side.

Mars 18 February 2021 - 08:52

Thank you Ken. Since the cold air shifted, we’re still struggling to get rooms back to temperature at the north despite the milder temperatures at around 10C. We think it’s flow related, and are getting someone out to have a look.

ken B 18 February 2021 - 12:28

Another factor is the high thermal mass of the building which will take days to reach a new balance point input/heat loss particularly with a low energy heat source. My guess is that the new balance point will only increase by the order of 1C /day. Perhaps relatively easy to increase the air temp even with draughts but as soon as the heat source is removed the temp sinks. In winter i take note of my interior wall surface temps using a laser thermometer.
The air can be warm enough in theory but you do not feel warm because the walls are rediating cold (in laymans terms)

Derek Marsh 20 February 2021 - 09:14

Hi Ken B,

Whilst I was looking (though it was a few years back) at the various meters available in the market place at the time, dual tariff meters were certainly still available. I fully appreciate what you are saying about the meter quantifying usage over each 30 minute period, which happens to align with how the electricity trading market operates. What I would question is how would the smart meter function for someone who is on a dual tariff contract and then decides to change supplier, where the new supplier cannot read their particular smart meter. Unless all the smart meters now have standard communication protocols, then it would potentially require the smart meter to be replaced every time you change supplier.

Tabula Rasa 19 February 2021 - 09:49

I’d love to have a heat source pump but would probably think of it as a whole off grid package ie also using solar, wind and battery to capture electricity which would negate some of the risks of rising costs whilst also meaning a bigger upfront cost.

Mars 19 February 2021 - 12:18

We have solar PV with our ASHP, and wind is definitely a worthwhile addition. That’s something that’s on our radar.

Derek Marsh 20 February 2021 - 14:48

Hi Mars,

I noticed on one of your photo’s that you have a pond or lake. Did you not consider a GSHP system with a collector plate in the water. Since water is most dense at 4C, then the bottom of the lake should not really fall below 4C unless the lake freezes solid. The ideal of course is running water, which would carry the cooled water away from the plate and replace it with warmer water.
I looked at wind turbines (but not in great detail). Their output power compared to solar is quite low, but of course they still generate when there is no sunlight.

Mars 20 February 2021 - 14:58

We only found out after installing our ASHP that such a thing as “water source” existed. To be honest, I’m not sure whether we would have pursued it, but it is something that continues to linger in the back of my mind. We have, however, invested in the ASHP so it’s difficult to not continue using it, unless there was a way to “merge” the ASHP and “water source”.

Our pond is a water course, because water leaves it at the bottom and is fed by other ponds above it, so water is always coming through it, at a reasonable rate too, especially during the winter.

Andrew+Scott 19 February 2021 - 12:47

I agree that the government have a significant problem in encouraging people away from fossil fuels for domestic heating. According to the Energy Savings Trust, energy types all based on per kWh are currently averaging 3.75p for mains gas, 5.25p for oil, 6.75p for LPG and of course electricity at around 16p. On a cost basis electricity is just way too expensive. However, demand is high and infrastructure is ageing and barely coping, so the need for investment means that costs are unlikely to be subsidised or reduced any time soon. We will probably see costs increase for gas and oil through taxation, which I would think are a tempting target for the treasury at the moment, but will be incremental to wean consumers off fossil fuels. So the only option really is to incentivise more private micro-generation. I think that the best way is grants for solar and wind generation and increased FIT payments.
From a personal viewpoint, bearing in mind we have no mains gas in our area, Solar PV combined with a GSHP was the most economic and future proof option and has proven to be so. Obviously it is not reasonable to make judgements on purely monthly costs as seasonal variations have to be offset. On an annual basis, we consume on average 10.75 kWh from the grid, and we generate 9.67 kWh from our solar PV (3.5 kW system). Therefore with our FIT our actual energy costs are for just under 1 kWh/ day.
If we consider our peak consumption last month, Jan 21, it was 692 kWh or approximately 22 kWh per day, or 1 kWh/hr which ties in with our SAP and GSHP calculations. Our house was calculated to require 6 kWh/h of heat to maintain 20 deg. C inside whilst -5 deg. outside. External temperature has probably averaged +3 deg. so demand would be somewhat less than 6 kW/h. From the heat input side of the equation, our heating being the main energy demand has been say 0.8 kWh and with a COP of 4.5, results in a calculated heating demand of 3.6 kWh which correlates the theoretical design with actual measurements and conditions. We have plenty of spare capacity to increase our temperature if required, although 20 – 21 deg. is fine, and we have a timer controlled immersion heater used to give a daily boost to our hot water around 13.00 – 14.00 hrs when our solar PV is at maximum output. The result is we are never cold or short of hot water.
I realise that we were in an ideal position to design and build our house to full building regulations, and control the quality, and many will not have any engineering knowledge. However, there is no reason why we should continue to allow house builders, heating designers and installers to get away with not providing adequate and easily understood information, performance guarantees and quality support. It is unacceptable, it isn’t rocket science, and some form of industry standard is required to accompany the SAP, EPC for a property with energy consumers installed. Perhaps an IEPC (Installed Energy Performance Certificate)

Mars 19 February 2021 - 22:42

Incredibly interesting Andrew. Thanks for sharing. Your numbers are amazing, and inspiring.

Your comments about builders, installers, etc. are also bang on target.

Derek Marsh 20 February 2021 - 10:10

Hi Andrew+Scott,

I fully agree with your sentiments concerning correctly assessing heat load, thermal efficiency etc. before and during the planning stage, followed by correct commissioning and optimisation after installation. As an Engineer myself, you will probably agree with my concern, over the years, about the quality of training and performance that many ‘so called Engineers’ seem to display. If anything the standard seems to be falling rather increasing, with many more ‘talking a good job’, rather than performing one.
I would be interested to know the manufacturer and model of your ASHP that achieves a CoP of 4.5.
I would suggest (when time allows) it would be useful for you to compile as list detailing equipment manufacturers, system installers etc, along with customer assessments of the quality/performance of equipment and ease of use and the performance and reliability of installers and service companies. This would certainly aid people like myself who are thinking of going down the ASHP route in making informed decisions.
As an example, I think it was back last November when I was contacted by a company about ASHP’s. Having been ‘around the block’ a few times now, I don’t normally entertain cold callers, but I thought ‘lets see what they have to say’ and I may be able to have a bit of fun in the process. To cut a long story short, this guy turned up, stated that a 5kW system would cost £11k, though we got it down to £10.5k by not replacing the radiators. So with the grant of £5k would cost £5.5k. When I asked about the ASHP and how much they cost, he tried to convince me that an Ecodan of that size was in the region of £4k. When I pointed out that I could actually purchase the exact same model for less than £1k, the guy got quite aggressive and walked out. A list of reliable and trustworthy companies would therefore help protect potential buyers from the less reputable ones.

Julian+C 19 February 2021 - 14:53

Thanks for update YouTube 6. Interesting, and difficult, that your ASHP has perhaps struggled when it gets down to -6C. Is it either the wrong ASHP, better insulation required or not set up correctly.
On the vid, you did mention your EPC was D heading to C? That could have an impact? Have you had your instalers back to adjust any settings? Your Global Energy Systems ASHP is quite a large unit (I guess required because you have a lovey, large property). Is there an indoor element to it? Can I ask why you chose Global Energy Systems over Mitsubishi, Daikin, LG, Stiebel or any of the multiple supplier? That is my complaint about the G/ASHP industry – there are no comparison tests (I think I noted elsewhere in your blog). If you are buying a washing machine, fridge, home speak, phone, car – there are umpteen test reviews. Telling what they do well, what they do badly, comparing to competition. ASHPs nothing! Other than “we use inverter tech” – they all do now. “We use R32 refrigerant” – they all do now. Anyway rant over 🙂 I do appreciate both your views and reviews. Thank you. I’m still thinking the Daikin is best for me – but only because I have had the best support from their installer. Not because someone has test driven a Daikin in a glassy bungalow in rural Worcestershire and said its the bees knees.

Mark Crooks 19 February 2021 - 18:04

8th Jan.
The ANSI (Average North Sea Index) price has now risen by more than 20% above where it was when you signed your supply agreement, and therefore we are left with no alternative but to implement a 6.7 pence per litre temporary surcharge on the price of your LPG. This will be with immediate effect.

19th Feb.
The US normally export 50% of the product that they produce to world markets, including Europe and Asia, but due to internal demand in the states, this is currently not happening.

Markets have been increasing over the last few weeks and now these additional costs can no longer be absorbed. Therefore, we are left with no alternative but to implement a 6.2 pence per litre temporary surcharge on the price of your LPG. This will be with immediate effect.

29% increase in the cost of LPG over 2 months. Perhaps this makes a 16pp kWh tariff slightly more palatable. 🙂

Mars 19 February 2021 - 19:31

Wow. That’s very interesting. We have some neighbours down the road that are on LPG and they were complaining about rising prices of LPG last year, so this is going to make matters even worse. Hmm.

Julian C 19 February 2021 - 21:16

Oil is 41.99p/L thru my local buying collective. It keeps increasing in Winter. But reduces somewhat in summer. But only keeps increasing overall.
Let’s hope the government adjusts the gas taxes

Mars 19 February 2021 - 21:43


ken B 20 February 2021 - 10:06

Wonder why you did not choose a GSHP as you have the land. They dont suffer from the winter weather and give better COPS all round.

Mars 20 February 2021 - 10:16

We did consider it but opted not to because the installation and upheaval would have been immense, and we had plans for the field to plant an orchard and grow veg. The price was also prohibitive, as we were potentially looking to outlay over £25,000. Yes, the RHI payments are also sizeable, but it’s one of those decisions you have to take. To my understanding the refrigerant in the ground source coils also needs to be replaced every couple of years which is a large job.

I still think ASHP is the right play for us, but it’s a matter of getting the flows working as they should.

Slartibartfast 6 April 2021 - 12:28

Have you had the heat pump set up properly by someone that really knows what they are doing? We had a MAJOR problem with our heat pump as the idiot installer managed to get all the settings wrong. Like you we had replaced an old oil boiler with a heat pump and we were led to believe that the heat pump would save us money especially as oil prices were certain to rise over the years.

Our first winter the electric bill was enormous and way more than our old oil bill. I tried to get the installer back but he had done a runner and was no where to be found. Luckily I found a bloke that really knew about these things and he spent about half a day changing the settings and testing the thing and he mentioned that the original installer was an idiot who had set just about everything up wrongly. Luckily the plumbing was all OK and the next winter our electric bill was way less and the house was just as warm. The heat pump is not doing exactly what we had been led to believe it would do from the installer so it seems clear to me that the setting up of the thing can make a world of difference to how much it costs to run.

I would guess that there are a lot of old heating blokes around that are now bunging these things in without having the knowledge needed to set them up properly for the particular installation and weather conditions. Our bloke said one of the main problems he finds is these things set up for the wrong climate as many are imported and the factory settings are not right for our weather. I have no idea if that is true but I do know that changing the settings really transformed the way our heat pump works.

Jeff 24 May 2021 - 18:58

Our house is about 100 years old in a conservation area. So all the usual challenges regarding installation that many posters have mentioned that can be overcome to some extent but probably not completely. Neighbours in the same constructed properties have attempted various things with mixed success and new damp issues so we will have to be careful if we do anything.

It is fine with a modern mains gas boiler and a 5kw log burner but we are starting to think about the future.

It has been interesting reading the posts and understanding peoples experience.

It does make me wonder if ASHPs are going to be the best option for our house when we do have to remove the gas boiler in years to come.

The idea of keeping a house like ours with our usage relatively warm all the time seems counter intuitive.

In the week we don’t bother with heating in the morning and turn it on in the evening when back from work basically. This last year has been different with lockdown. The high temperature heating of a gas boiler or log burner work great.

To a lay person it can feel like a technology being shoe horned into solving an issue.

Perhaps this is the new future and we have to get use to it and adjust. I can’t help but think a high heat solution for a limited time might work out better for some situations. I have a lot to learn obviously.

Mars 25 May 2021 - 07:52

Good morning Jeff. You’ve raised some interesting points. I would like to invite you to join Renewable Heating Hub where you can participate in our forum and where others can share their views on the points you’ve made: https://renewableheatinghub.co.uk/forums

I’d recommend copying and pasting your comment into a new forum discussion.

Schmitt Trading Ltd 29 June 2021 - 11:12

Thank you very much for this helpful blog post. Do you mind reblogging?

Mars 29 June 2021 - 12:14

Thanks for the feedback – feel free to reblog this post if you’d like.

Schmitt Trading Ltd 29 June 2021 - 12:42

In Germany, the energy price has risen up to 32 Ct/kWh for the standard tariff (worl champion).
We paid 2000 € with
7568 kWh for heating with our heat pump in 2020. This equals a “special heat pump tariff” of 26.38 Ct/kWh.
Back in 2002, we started with a medium tariff of 11.8 Ct/kWh.
We must consider how to go on as soon as the heat pump breaks down…

nick peaty 30 June 2021 - 17:55

Lots of doom and gloom in the comments regarding the inevitable rise of the cost of electricity. It need not be so – in same way that we have seen data costs go from a per megabyte cost or phone calls costed per minute to a an “all you can eat” subscription model then some experts believe that the same is going to be true of energy costs over the next decade.
A glut of renewable energy coupled to huge energy storage systems could lead to an abundance of very low cost energy.
Tony Ceba has been spot on with his prophecies over the last 25 years regarding the death of coal and now oil and gas as well as the transportation revolution that is now irreversible.

Be of good cheer and read his new paper on Super Power here – https://www.rethinkx.com/press-release/2020/10/26/new-report-rethinking-energy-2020-2030-100-solar-wind-and-batteries-is-just-the-beginning

or on Youtube here https://www.youtube.com/watch?v=PM2RxWtF4Ds

Schmitt Trading Ltd 1 July 2021 - 10:03

Hi Ken,
I would love to buy cheap energy from my local community supplier.

The actual spot price at the stock exchange is 61 Euros per Megawatthour which equals 6.1 Cents per kWh.

Germany is notorious for bureaucracy and high taxes.

This is why I do not believe in cheap energy prices.

I would also accept fair prices, e. g. 100 % on top of the wholesale price which equals 12.2 Cents.

Then I would buy my next heat pump and run it for 20 years.

But the price must remain stable.

I would also accept inflationary price inreases by 2 % a year.

But I rather expect a total retail price between 35 to 50 Cents in the next 20 years.

This is unbearable.

Roger Ball 12 July 2021 - 20:57

Looking for advice as viewing a property tomorrow heated wholly by ASHP.
This 4 bedroom detached property was built in 2017 and the ASHP system fitted by the builder (Bovis)… in fact the whole estate is heated that way.
The house has probably the best EPC rating I’ve ever seen – everything, including the concrete floors and windows are classed as”very good”.
The ASHP is an Mitsubishi Ecodan and is apparently very efficient.
This is a long shot, bit any ideas on heating costs for this house?

Mars 13 July 2021 - 16:43

That all sounds really exciting and the EPC ratings are fantastic. I wouldn’t be able to guess the heating costs on this. It’ll also come down to what target temperature you want to maintain across your property. What I would recommend is that you create an account on the forums at Renewable Heating Hub and post your question there to get assistance, as there will be homeowners with similar specs and homes that can give you a far more accurate gouestimatte: https://renewableheatinghub.co.uk/forums

Barbara Vincent 5 October 2021 - 18:05

But the renewable hub website doesn’t work.

Mars 5 October 2021 - 18:09

It is working Barbara. https://www.renewableheatinghub.co.uk

Barbara Vincent 5 October 2021 - 18:18

Oh so it is. Last time I logged on it said site was up for sale?

Mars 5 October 2021 - 18:19

Great. We’re not selling the site. May have been the wrong URL. 🤔

Barbara Vincent 5 October 2021 - 18:32

Yes , knowing me , I probably have.

David B 10 September 2021 - 19:29

Great blog, thanks.

I’m in the difficult position where I’d very much like to replacing my ageing oil boiler with an ASHP, but I just don’t see how it’s viable, financially.

Putting aside the fact that the initial outlay is so high, my energy supplier is going to raise my tariff to 20.471p per kWh from 01/10/21!

It’s just not doable.

J Sykes 5 October 2021 - 17:12

Hi, I’d like to share my concern and hopefully get some practical advise.

We had our Ecodan ASHP installed just over 2 years ago to replace our gas combi boiler. At that time were paying around 13p per kWh for electricity. Over that past few years, even though the price increased to around 14.5 per kWh, we were still paying, on the whole, a similar price of around £1450 per annum (approx 10,000 kWh annually).

Up until a couple of weeks ago we were with Igloo who unfortunately went bust. Today I received an email from Igloo introducing me to my new supplier E.ON. who’s tariff is a staggering 25.63 per kWh….. (yes you read that correctly). This means an estimated annual increase of over £1000 (and that’s if we are careful). How is this sustainable??

We signed up for this new technology the on the presumption that gas was being phased-out and would become significantly more expensive over the coming years whereas ‘clean’ electric would remain more stable on it’s price.

I’ve just contacted the installer Greener Living (based in Sheffield) for some advice to hear what they are proposing to advise the customers who has the ASHP installed by them, if feels like they should have some response or advice … they had nothing to offer other than what I already knew.

Do we really need to seriously consider a secondary heating system? Can anyone provide some advice?

Barbara Vincent 5 October 2021 - 18:03

Good luck. This is our 1st winter with an air source heat pump. I think we are just going to have to ride the storm and see what comes out the other end.

Mars 5 October 2021 - 18:10

It’s going to be an interesting year.

Barbara Vincent 5 October 2021 - 18:35

Just transferring to Octopus. Need meters changing but heaven knows how long that will take.
Tarrif will be obsolete by then.

Jenny Ross 5 October 2021 - 19:19

You don’t need to stay with EON. Shop around for a better tariff.

Mars 5 October 2021 - 20:51

I don’t there are going to be many deals for the weeks ahead. If anyone finds a great deal, please share.

Jenny Ross 5 October 2021 - 21:22

Yes I see what you mean Mars. Definitely quite critical for those who have been moved because their current company has gone bust. With COP26 playing out in the background government is going to have to do something radical to incentivise the alternative, renewable energy market.

Barbara Vincent 7 October 2021 - 10:04

Yes, please do.

Charles McHardy 13 October 2021 - 08:24

I am in Aberdeenshire and am about to start construction of a house and have to make a decision on the heating system. I am being pushed in the direction of an ASHP and am unsure whether I should go down that route or what I am more familiar with, i.e. oil central heating.
While understanding the need for each of us to do our part in terms of minimising harmful emissions, I want a system that fits our needs in terms of providing us with heat and hot water when we want it while having a reasonable capital and operating cost.

Some thoughts/facts:
– The house will be very well insulated and, while not a passive house, pretty well sealed.
– We are deep in the countryside and in a, typically, fairly windy location.
– Within reason, I am more concerned with the capital cost than the operating cost.
– While spending quite a bit of time at home, when we do travel we do not want to wait several hours to have the house up to temperature on our return.

As I said, I am being pushed in the direction of an ASHP but my gut tells me that I should go with oil. I am also concerned that, if I do choose oil, I will be penalised by the building control department and, potentially, required to make modifications to the house (even more insulation for example) and install a solar panel array.

I am an engineer but a novice in this area and so wanted to reach out for any advise that other, who are more experienced and knowledgeable, might be able to give.


Jenny Ross 13 October 2021 - 10:29

From a carbon footprint point of view please don’t choose oil if you can avoid it. 😊
We have just had an ASHP installed. We are also deeply rural in eastern Scotland and our home is reasonably well insulated. So far the ASHP is operating far in excess of our expectations. It doesn’t take ‘several hours’ for the radiators to warm up. Within 15 minutes they are beginning to warm and within 30 minutes they are hot – and I mean hot. We have ample amounts of very hot water. Only half of our radiators were resized and changed.

In terms of capital costs the ASHP was cheaper to install than the quote we had for oil installation (£11k in 2018) and the running costs are about two thirds less than our previous electric boilers.

I would like to see a winter through to assess how the heat pump operates when temperatures outside fall below zero for extended periods of time but so far it has definitely made financial sense for us and our home is wonderfully warm – something we are definitely not used to.

I am sure that the operative efficiency of the installation depends not just on the type of heat pump but also on the knowledge and competence of the installer and the correct calculation of heat loss etc.

As to energy prices – my view is that these will settle in due course but at a higher level. For decades we have had cheap energy but at an unsustainably high cost to the environment. I worked previously as an environmental economist so I would say that.

Thimbles 30 October 2021 - 18:43

Very good point. I have just done the energy calculations for a heat pump to replace our oil boiler that supplies 21,000 kw per annum ( about 2,100L/yr of oil) for water radiator heating and hot water. I did the calcs on a monthly basis using average day and night ambient temperatures and near-peak daytime temperatures for Summer months ( to efficiently produce hot water). Based on our current pricing of 50p/L for oil and 14p/KWh for electricity the answer is the 2 systems are broadly the same annual operating cost ( before grants etc) for our old detached 4 bed farmhouse in the south of England. When we come off our fixed price electricity price in April I would expect the ASHP running cost to be slightly higher than oil. Based on my calcs the annual average COP is 2.4 but achieving this is highly dependant on configuring the system in an optimum way and you need to understand the Installation Guide in some detail to do this. Getting good COP data curves for ASHP units and understanding the system operating points is essential to get the calcs correct. As ever the companies selling ASHP installations are quoting unrealistic numbers and the standard SCOP calcualtion basis does not seem to help – too optimistic. I will probably proceed with the ASHP for simplicity and environmental reasons but if cost were the criteria I would not be considering ASHP with my setup. The RHI grants do not cover the differential installation cost for ASHP so if you add in the additional cost of capital for the ASHP system it becomes even less economically viable.

Barbara Vincent 31 October 2021 - 12:09

That’s very true. There are companies making it look like there will be a very good return on the rhi form ashp.
I was told I would get over £1000 a year when in fact I will get I will only be getting £684. Hardly going to be a windfall. I’ve be taken for a Mug!!

Mars 1 November 2021 - 15:26

Sorry to hear that Barbara. Do you have metres connected to your heat pump that pay you on the heat generated or is it a set figure. I would definitely register this as a compliant with the MCS if you’ve been promised a different amount of money from the installer. Do you have it in writing?

Barbara Vincent 1 November 2021 - 18:46

I have the estimated figures that the salesman used to sell the system to me.
I have a meter that has ‘rhi’written on it and one with ‘water heater’ on. Does that mean that someone from the RHI will contact me for this reading or do I go by the amount on my rhi account?
As I am a novice with this system It’s all new to me.

Mars 1 November 2021 - 21:03

When was your account with RHI set up Barbara? I’m not familiar with your metering set up. We have two metre – one for electricity used and one for heat generated. This is because we retained our oil boiler. I assume you only have a heat pump now. We have to sign in quarterly and submit our data, and get paid different amounts.

I’d call RHI to get confirmation on how you’re set up, and then call MCS to lodge a formal complaint.

Barbara Vincent 2 November 2021 - 07:45

Thanks. I still have my gas water heater and 1 room heater in sitting room still in situ. I have turned the gas off for now.
I know when I started the rhi it was not set up for metering and monitoring. I have 1 meter for heat pump and 1 for when the immersion heater comes on. The heaters went on last night but as it’s all new I haven’t got the hang of all this yet. They didn’t warm up last night as probably hadn’t turned the dials round far enough.
Day off tomorrow so will find out more.

Mars 2 November 2021 - 07:53

Good luck Barbara. Keep us posted.

Mars 1 November 2021 - 21:05

If you’d like more input from other heat pump users, please feel free to join our forums here: https://renewableheatinghub.co.uk/forums

Mars 1 November 2021 - 15:29

Valid points Thimbles. The selling supporting numbers are very easy to tweak – our numbers were accurate for the first two years, but with the spiralling cost of electricity tariffs our numbers are now very out of kilter. Oil is much cheaper to run now.

Mars 15 October 2021 - 08:23

Morning Charles. To get a better response I’d like to invite you to join Renewable Heating Hub (our sister site) where you can participate in our forum discussions and get answers to questions about renewable heating and heat pumps https://renewableheatinghub.co.uk/forums

Grant 8 November 2021 - 15:43

We live in an old stone farmhouse in France heated by ASHP and wood burner with a back boiler. Our usage and bills are similar to yours.
ASHP are very good for a well insulated property but seem a folly in old buildings.

We have UFH downstairs and rads and wood burner upstairs (upside down house of around 220m2). I’d be interested to know the floor area you are heating?

we spend over €3000 a year on electricity and would love to cut that both for financial and environmental reasons but we have more questions than answers:
should we insulate the roof more?
is too much heat escaping through the stone walls?
would photovoltaics or solar tubes be cost effective?
is the ASHP set up correctly?

the last one is probably the biggest concern. There seems no way of knowing or checking it’s working correctly or to change the settings.

if I knew then what I know now I’d have gone for a different system.

Thimbles 8 November 2021 - 18:12

Without knowing your system and its setup its not possible to comment on if it set up efficiently. However I would have said that unless you are at high altitude in France your ambient temperatures should be better that UK ambient and you should be getting good efficiency. I have now recalculated my proposed system using better COP data from a current Nibe unit and I can significantly improve the economics. The key parameters that will get you efficient operation appear to be:
1. Run the water temperature through the heating system at 45C or lower – this may mean increasing your radiator sizes in rooms you always want to keep at 20C or warmer.
2. For overnight background heating drop to a 35C or lower water temperature
3. Only heat the hot water during the middle of the day when the ambient temperatures are highest (or beter still use solar tubes to provide hot water).
The ability to be able to configure your system to do the above (and probably to fine tune it thereafter) would appear to be essential and seems to provided in most of the current systems I am looking at.
Item 1 has by far the greatest impact as it typically represents ~80% of the annual heat load, probably followed by ensuring you have adequate insulation. By reducing the water temperature for winter heating from 55C to 45C I increased my SCOP from 2.8 to 3.5 which is a 20% reduction in electricity costs.

Grant 9 November 2021 - 08:07

Thanks for the feedback Thimbles. We have an Airmat/Daikin pump and there is no control panel to alter water temps and so on. It was set up via laptop by the installer and the only controls we have now are via thermostat (so basically on/off).

Our winters are often colder than U.K. While we are quite far south and only 600’ up we don’t benefit from the sea being nearby which tends to make the U.K. more temperate. For example it’s 2 degrees this morning and we’ve seen close to -20 in the winter.

After much research we opted for Jaga Strava radiators for low temperature performance.

Thimbles 9 November 2021 - 09:48

I am looking at a Daikin Altherma 3 system which seems to have all the control flexibility I need to configure it to run efficiently but I guess your system must be older . Without this flexibility I would not be considering ASHP.
Being old our house is not that well insulated but my experience tells me that draughts give you more heat loss than poor insulation. Our house was coldest when the wind blew rather than when the outside temperature was low but the air still. This is because every m3 of cold air entering the house is displacing a m3 of warm air and if your air change rate is high then you lose a lot of heat. By elminating draughts, particularly on the side of the house facing the prevailing winter winds, I made big improvemnts to the energy losses.

Grant 9 November 2021 - 13:33

Thanks. That’s a good tip about draughts.
Our system is 11 years old now, good to hear the new ones are more controllable.

Brian Pedley 13 November 2021 - 00:09

Please can I join your forum?

Mars 13 November 2021 - 08:20

Of course you can. Please simply head over to https://renewableheatinghub.co.uk/forums and create an account.

Lily S 20 November 2021 - 17:43

Hey, people: please do not give up on air source heat pumps!

I’ve recently put an air source heat pump into my end of terrace 1960s London house, having managed to navigate the green homes grant system and get a £10,000 grant to help me install one. (Nb: I also had to have larger radiators put in.)

My main reason for going for an air source heat pump was the fact that we’re making the planet unsustainable for human and much animal and plant life. I have children and I’m terrified about the world they’re growing up in.

However, lower fuel bills would be great. I was paying *£1,900* a year for gas and electricity when I had gas boiler! That included my leaving the heating off on some wintry days when I was at home but the kids were not around.

I have realised that my 1960s house is shoddily built – it’s cold in winter and hot in summer. (I lived in a Victorian end of terrace before and it was much better in both summer and winter and my fuel bills were much lower.)

So far, looking at the costs during the cold spell we’re now having, my annual energy costs with an air source heat pump are likely to be just over £1,300. Still huge but considerably better.

I’m having solar panels and new windows installed, which I hope will help with costs. (I haven’t won the lottery. I have no savings but got a pay-off after from a former job which worsened a disabililty. All the pay-off has gone on this ‘greening’ of my property.

I’m also on the look out to make this house yet more energy efficient. LED lights rather than older energy efficient bulbs will come next, when I can afford another round of greening.

Supplier-wise, I’m with Good Energy (100% renewable electricity) and I can recommend them. I looked at Octopus but they advised me not to change as their rates are higher. (I appreciated Octopus’s honesty!)

And I agree that we need energy companies and the government to offer incentives to ensure that home owners switch to low and zero carbon energy charges.

Mars 21 November 2021 - 21:26

Thank you Lily – some excellent points. We would like to invite you to join the forums on our sister site – https://renewableheatinghub.co.uk/forums – so that you can share your experiences and interact with like-minded people.

Chris 22 November 2021 - 09:29

One thing I learned many years ago, is that if a Politician says something is in “your best interest” then do the complete opposite. Politicians aren’t Saints or your Mum, and Energy Companies are businesses with a sole aim to make money, common sense says they won’t be advising you to do something which will lose them profit, that would be like Sainsbury’s telling you to go and do your shopping at Tesco!!, so when both tell me to fit ASHP, then I question why, and your own experience of using one, tells me that is right!. I hate to think how much its costing you with Electricity prices at 21p per kw/h currently and set to go even higher next spring when the energy cap is reviewed again.

The problem in the UK is, that despite £billions being spent on renewable energy, it doesn’t make up the shortfall lost by the decommissioning of the original Coal Fired plants, so we are something of an island which is Energy Bereft, when the Sun doesn’t shine and the wind doesn’t blow – which can be for several weeks at a time. This makes us more reliant on importing power from Europe using an inter-connector, and burning Gas in Gas Turbines to generate Electricity – Yes we really do burn one fossil fuel to produce another – hence why its so expensive, especially as we have just lost one under sea inter-connector due to fire, meaning even more expensive Gas needs to be burned.

Until a time where Nuclear Power Stations can be built or Coal Fired ones are brought back online (Unlikely, despite Germany keeping theirs until 2038!) Electricity is ALWAYS going to cost far more than Gas, because we are burning Gas to produce it, and evena COP of 4.5 can’t equal Gas being sold at 4.1p per KW/H.

Also remember that the COP rating of your ASHP which can be as high as 4.5 in the glossy Brochure is measured at 7c and under ideal running conditions, once that outside temperature drops, so does the COP rating, meaning its only 2 or 2.5 at best when its -7c outside, and given ice days and -10c nights are very common in large areas of the UK during the Winter months, that means your ASHP is the least efficient and the most expensive to run at the time when YOU NEED IT THE MOST!.

Until Electricity drops below 10p then ASHP is not going to replace Gas Central Heating in areas which have that option – at least not cheaply or like for like in running cost, and anybody who thinks otherwise is deluded (see opening paragraph), and the running cost, doesn’t include the cost of installation, or having the space for a massive heat store (many households originally removing their hot water cylinder to free up space, now needing to find room for an even bigger cylinder).

That also doesn’t touch on the cost of the uber levels of insulation needed to make hot water of around 46c, heat a room, in say a 1930 built property. Before investing in ASHP, if you have thermostatic valves fitted to your existing Gas or Oil fired radiators, turn them down to the point where they are around 50c to the touch, if it heats your room to 20c or 21 then ASHP will probably be fine, if they don’t then you are going to need some major changes to the fabric of the building in the form of insulation!.

Jennifer Ross 10 December 2021 - 15:27

Hi Chris, You say that electricity is always going to cost more than gas because we are burning gas to produce it. Can you explain please how your statement fits in with the figures quoted by the Scottish Government, for example, which show that 97% of Scotland’s electricity was produced from renewable resources (onshore wind 60% of the total; offshore wind 11%; and renewable hydro 18%). Thanks.

Wilmarie 31 December 2021 - 12:36

Although I’m slightly relieved we’re not alone in the shock of the energy bills, I’m having a bit of a panic attack today after receiving the newest one. We moved in to a 4 bedroom house on a farm January this year, I was excited about the ground source heat pump as I understood this to be a much more efficient source of energy (I know it’s not air source but I have a suspicion it’s the same concerns).

It’s just myelf and my other half, but we each have an office in the house which is why we went big. In our previous house we paid around £110 for electric and gas combined, so I set my direct debit up for the same amount. My bill today, however, suggests that we’re £3436 in debit and I can’t believe that can be right! I don’t know whether to laugh or cry.

Barbara Vincent. 31 December 2021 - 12:53

Oh Cry.
Who sold you yours? Someone who was just out for the money not your interests.
There must be someone to complain to.

Mars 31 December 2021 - 21:20

If the installer was MCS accredited, there are recourse actions.

Mars 31 December 2021 - 21:19

Good evening Wilmarie. We’re so sorry to hear about your shock electricity bill. I’m surprised to hear it’s as high as that with a ground source system. More on that in a minute.

Energy tariffs started going up in Feb, leading to their autumn crescendo – for what it’s worth, gas prices have also shot up.

If you have the time and would like to see how to improve the efficiency of your heating system, I’d recommended you create an account on our sister site and post your case there – we’ll see if we can cut your bills a bit: https://renewableheatinghub.co.uk/forums

Mars 31 December 2021 - 21:33

As an additional point, if you’ve had your energy provider switched this year, I’d double check your tariff: https://myhomefarm.co.uk/check-your-electricity-tariff-to-see-if-youre-being-overcharged

ken B 1 January 2022 - 14:31

I am guessing your bill is based on an estimated reading and bearing no relation to reality You could provide an actual reading or go onto a Smart meter.
Ground source HPs are good no doubt about it.


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