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

by Mars
renewable energy heat source

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

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

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

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

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

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

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

Consumption highs and lows of our air source heat pump

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

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

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

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

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

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

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

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

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

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

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

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13 comments

Caernarfon 18kW Air Source Heat Pump Review - Autumn » My Home Farm 23 February 2020 - 21:31

[…] UPDATE Feb 19, 2020: the winter review is available here. […]

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What is a Renewable Energy Heat Source? » My Home Farm 1 March 2020 - 07:00

[…] There are skeptics as to whether ASHPs can be effective in the UK. Check out our winter air source heat pump review. […]

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[…] It’s been a year since the panels have gone up, and they have met our expectations. Our primary reason for installing a 6.16kW array was so that it could contribute towards the running costs our air source heat pump. […]

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We need to get more sustainable, pronto » My Home Farm 20 March 2020 - 07:02

[…] we have managed to get renewable forms of heating (air source heat pump) and electricity (solar PV array), our next big projects for this year are going to be getting our […]

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Accuracy of our air source heat pump proposal » My Home Farm 12 June 2020 - 08:28

[…] Another massive difference between the ASHP and the oil boiler is that with the ASHP our heating in the cold months runs 24/7 versus limited timings on oil. We’ve covered this aspect before. […]

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[…] on the path to sustainability with renewable heating, solar PV and our new veg patch, the weather has never been more important to us, so we’re very […]

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J Guenther 13 July 2020 - 23:49

Interesting.

Reply
Air source heat pump electricity consumption » My Home Farm 19 July 2020 - 07:21

[…] If you’d like more information on air source heat pump electricity consumption on cold sunny days versus warm overcast days during the winter you’ll find this post interesting. […]

Reply
Mark Rosher 22 August 2020 - 09:29

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

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

Reply
Mars 22 August 2020 - 22:07

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

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

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

Reply
Ed 24 August 2020 - 16:57

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

Reply
Mars 24 August 2020 - 17:02

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

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

Reply
From lattes and boardrooms to wellies and homegrown veg » My Home Farm 28 August 2020 - 08:10

[…] to keep your sewage treatment tank healthy, to big things like installing solar PV panels and an air source heat pump to get off oil central heating and using renewables to their […]

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