Our second winter air source heat pump experience

by Mars

We’re halfway through our second winter with the 18kW Caernarfon air source heat pump (ASHP), and it’s time for an update.

The biggest difference so far is that this winter we’ve fully committed to having the ASHP on 24/7 and it has made a difference. We have, however, noticed that when outdoor temperatures drop below 5C we start to see a difference in temperatures inside the house, and that becomes more noticeable when you edge towards 0C.

The chart below shows what we mentioned in the video, and you can see a clear pattern form between ambient temperatures and electricity consumption. It’s worth adding that we’ve maintained temperatures of 21-22C in all our main living areas and bedrooms, and the sole issue remains the TV room and guest bedroom at the far northern end of the house.


Mark Crooks 14 February 2021 - 07:39

Did you record this before your comments about electricity prices? You seem more positive than I was expecting after reading that post.

Mars 14 February 2021 - 07:53

Very astute observation Mark. Yes, that was very much the case. We have an update video coming out this week hopefully, addressing other concerns, because the temperatures dropped massively after we finished filming that episode.

Ron 15 February 2021 - 09:49

Great video again guys!

Just a thought I wanted to share with you:

You said that when the ambient temperature drops below 6C the climate in the house starts changing, it feels cooler. I don’t think that would be completely caused by the ASHP having to work harder to keep up with the heat demand of the house. I think that the heat loss of the house has a large contribution to this. IOW: the house looses it’s warmth quicker when it is cold outside. Would that make sense at all? …just a thought.

Mars 15 February 2021 - 15:26

Thanks Ron. I agree that our house loses heat at a faster rate. What doesn’t make sense is why our radiators drop in temperature, which I’ve started to monitor rad temperature as opposed to room temperature.

Mark Crooks 16 February 2021 - 06:37

Where on the circuit is the radiator that you are touching? If it’s the first to get hot water from the pump then I would be surprised it feels cooler if the flow temp is being reached. If it’s further along the circuit then this might make sense as each cool room would be drawing heat from the hot water passing through the radiators.

Mars 16 February 2021 - 08:22

We’ve still not figured out the circuit, but by looking at logically, it’ll be towards the end of the run. So it stands to reason it might/should be cooler. However, the heat pump should be heating the full circuit adequately, which it does at 6C and above, but not at 0C. That’s the mystery and frustration.

Peter Johnston 16 February 2021 - 19:55

Hi Mars,
I’ve been following your blog since I had a Samsung air to water 12kw heat pump fitted last October. I’m intrigued by your video and your performance you are getting. Firstly some background. My house is a bungalow and timber framed built around 1992. The loft is well insulated with no underfloor insulation and I stay in central Scotland in a wee village. Our heating was previously oil.

I have been monitoring energy use on a daily basis until this month when I went weekly. The past week we have had temperatures down to -15c with an average over the week of -7c, the temperature not getting above freezing. The main thermostat is usually set at 20.5c with individual TVR’s set for room temperatures.

Now coming to the performance of the heat pump. I will just use last week’s performance as this is pertinent to your comments. I used 253kwh of HP electricity over the week which equated to £34.86 cost for the week. The HP was able to maintain heat within the house at the set temperature. On our coldest night, I increased the thermostat to 24c mainly to try and offset heat loss due to the cold and to avoid frozen pipes. The heat pump managed amicably. I did have to do some maintenance, clearing snow that had covered a third of the pump. I also had a small build-up of ice, that eventually cleared its self.

I used to use 1000 litres of oil over the four winter months. So far cost are comparable based on oil at 40p/l, oil is now 45p/l. Like yourself concerned at the steep increase in electricity prices but I have got a new contract for 13.29p/kwh and Standing @17p from Symbio.

It’s certainly interesting to hear how different pumps perform and how setups can affect performance. I’ll contribute more about my installation and problems later. But for now, I hope you find this informative and many thanks for an informative blog.

Mars 16 February 2021 - 21:46

Thanks for sharing Peter. Very insightful and helpful. Just about to send you an email.

Gary Hardman 17 February 2021 - 16:45

Thought you might be interested in these videos about unheated cold weather greenhouses in Canada.

Three videos about using cold weather unheated greenhouses in Canada that copy a greenhouse design from northern China.

Oh and this Canadian guy kind of experimented his way into about the same design.

Ron 18 February 2021 - 09:58

For those who are on LinkedIn, here’s an interesting article: https://www.linkedin.com/pulse/retro-fitting-heat-pumps-non-domestic-buildings-chris-davis

Mars 18 February 2021 - 10:15

Nice find Ron. I’ll read it this evening.

Did our air source heat pump cope at -6C? » My Home Farm 19 February 2021 - 07:00

[…] when we thought we were rounding the corner of another mild winter, we were hit by freezing cold easterly winds in early February and our […]

Andy 19 February 2021 - 13:00

well you guys have certainly done your research and are sharing passing on so much REAL WORD useful information, we have 2 converted stone cottages made into one 3 bedrooms and one large landing room .about 125 square metres in all loft insulation and double glazing slate floors no other insulation only have an oil AGA for cooking and hot water and a multi fuel stove in the living area, have been considering a ASHP, but getting very put off by all the conflicting reviews out there some horrors of 800 to 900 pounds per month?? down to being able to heat their homes cheaper than gas and one running the whole lot for £190 per year with no fancy insulation?

I would trust forking out on an oil installation as the future for oil prices is very unpredictable probably with an out come far worse than the volatility of prices we live with today. If we can get time to look through and watch all your videos it may help us decide, the last point you raised is one that needs taking on board about reliability back up and repairs? I have never had an oil burner but NEVER had to repair or have a gas boiler serviced, they just seem to run on forever (i may have been just lucky) we installed a Gas combi and complete CH in a house we had back in the 90s simple to install and nothing inside that boiler that couldn’t be diagnosed or DIY replaced. If you do need to call somebody out it will not be cheap but will at least be easy to find and very quick. From reading i t seems like these air pumps develop a lot of issues and can only be repaired by specialist engineers from the manufacturing company only and may have to travel the length of the country even just to replace an internal fuse of adjust a setting, hence even the minimum call out can cost you hundreds or even thousands if something more serious has failed and the engineer has to come back again with the part, still toying with the idea but it does seem like this technology is not really user friendly advanced enough yet, probably really still in the research prototype stage. What are your thoughts on that? Would be interesting. Many thanks for your in-depth and informative videos. Regards, Andy

A big announcement: Renewable Heating Hub » My Home Farm 23 March 2021 - 14:47

[…] consistently grown our audience with people that are curious about sustainable, country living. Our air source heat pump and solar PV array has proven to be a big area of interest, and over the course of 2020 our content […]

Suzie 21 April 2021 - 19:46

We live in Surrey and moved into a bungalow with a Daikin ASHP installed in 2010. We have low temp radiators (no underfloor heating) with excellent insulation and our electricity bills are a whopping £300 per month. It is wall mounted and has always been noisy. When the temperatures dropped below freezing in the last few weeks, the ASHP wasn’t producing the required heat. It took two days for us to contact an engineer to come and take a look. I understand Daikin have made a lot of people redundant recently. The call out charge is £240. First we were told we needed a new compressor. They called to give us a price and said there were no compressors in the country. It would take 6 weeks to order and cost £1800. When we queried this, they said we could regas and see if that helps. It cost a further £660 and nothing works. Now when we turn the unit on the switch trips cutting off electricity to the entire house. They have now quoted a further £1500 to replace the PCBs etc. So, we have now sunk £1000 into a unit that will take at least several thousand pounds more to fix.
We had similar problems with an ASHP at a rental house – huge bills and house not warm enough in the winter.
I notice that people post glowing reviews of new ASHPs but I would suggest there aren’t enough ‘old’ units around for people to get an accurate idea of long term efficiency and effectiveness. Both our experiences are overwhelmingly negative. The callout charge when something goes wrong is beyond the budget of most families.
Rather than spend any more money on remedial work for the ASHP, we are going to install an oil tank and new oil boiler. We expect our energy bills to drop by at least 50%.


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