Air Source Heat Pump Performance for 2020

by Mars

We recently spoke about the general performance and efficiency of our air source heat pump (ASHP), but with 2020 behind us, we have a full year of data that we can now share.

From January 1-December 31, 2020, our ASHP consumed about 11,468kWh of electricity to drive our central heating running and heat up our hot water. Our electricity tariff for 2020 was £0.15/kWh which means that we spent around £1,720 on our heating last year.

Not surprisingly, given how awful the weather has been, December was our heaviest month because the weather was cold and humid, requiring the ASHP to work harder with more frequent defrost sessions.

In December, we used about 1,756kWh of electricity to run the air source heat pump, and at our rate of around £0.15, this equated to £263. As mentioned in many of other posts and videos, we were spending £250/month for oil to heat the house, but it was only being heated for certain periods during the day, versus our ASHP that runs 24/7.

So even though December was a little bit more expensive, this is something we can certainly live with because we only paid £162 to heat the house in November and £155 in October, compared to £250 for every autumn and winter month when the oil boiler was our primary source of heating.

air source heat pump performance
The spike on December 2 was a data collection glitch that took the previous 5 days’ data and added them all together.

Staying on the subject of oil boiler versus air source heat pump, we mentioned that our overall heating bill for 2020 was £1,720. In 2018, when the boiler was running, we spent £1,750 on oil to heat the house and water for just seven months. This in itself is quite the saving.

We’ve also recently switched energy providers (we will post a review during the course of January), which will take our tariff down from £0.15 to £0.10 per kWh. This will hopefully result in additional savings on our central heating and general electricity usage.

In case you haven’t seen our series on air source heat pumps, we’ve embedded three episodes below that discuss why we opted for an ASHP, what the installation entailed and our system’s performance and efficiency.


Mark Crooks 2 January 2021 - 08:30

Is your average indoor room temp really around 28ºC?

Mars 2 January 2021 - 08:33

No, that’s just the reading from our utility room cupboard where the control panel for the ASHP is located. It’s a throwaway number. Our average indoor temperature is set to 21-22C.

Steffan 2 January 2021 - 11:08

Happy New Year! Very little booster (direct heating element) heating used this year so that is a good result as it shows your heat pump has mostly been working as it should as a heat ‘mover’ from outside to inside. Could be some cold days coming up though…

A next step to reduce your energy use even further might be to figure out if you can afford to have a setback temperature at night (thats a lower nightime temperature in the house). [I wouldn’t be surprised if you were fed-up of talking about heat pumps though ;-)]

Mars 2 January 2021 - 21:17

Thanks for the feedback Stefan, and the best to you and your family in 2021.

Regarding the setback temperature, do you mean dropping the flow rate in the evenings or dropping thermostat temperatures?

Ron 2 January 2021 - 17:12

Thanks for sharing your data Mars! That’s really interesting. We’ve had our ASHP installed in December 2020 and until now I am quite worried about our E-bill to be honest. For example on 30-12-2020 we’ve used ca. 54 kWh. I guess I have to spread the costs over a full year to come to a monthly average.

We are with E-On at the moment on a one tariff meter (3-phase) and are paying £ 0.16782 per kWh. Would you mind sharing your E-supplier?

Mars 2 January 2021 - 21:15

Thanks for the feedback Ron. Given how cold it’s been, 54kWh is not that bad. How big is the space you’re heating, and are you leaving the pump on 24/7?

We’ve just switched electricity providers about a week ago to Symbio – their tariff is a little over 10p. Our last tariff with GOTO Energy was increased to 16p, which prompted us to switch.

Ron 3 January 2021 - 11:10

Our ASHP is only used for UFH. we’re heating up 183 m2 (ground floor and first floor). This is divided into 10 zones which each have their own room thermostat. The temperature set point of the ASHP is 40ºC and the system is on 24/7, we don’t turn things down in the night or when we are away from the house.

It’s a new build brick and blocks buildings with 150mm full filled cavity insulation, double glazed windows and a fully insulated floor and roof . We’re also using an MVHR system and have tried to build as airtight as possible. I just expected to use less electricity on the ASHP I guess.

Thanks for the tip on the energy supply! I will definitely look into this.

Mike Hyland 15 January 2021 - 11:14

Hi Ron. Probably worth understanding a couple of points. We too have UFH heating and the same ASHP as Mars from Global Energy. I’ve noticed that when we turn on the UFH heating (that was back in October for us) then it takes a very long time to get the floor (and everything touching the floor) up to temperature (it’s the thermal mass). During that time the ASHP is being worked quite hard and demands more electricity (obviously). Once everything is up to temperature then it all calms down a bit and the demand is more regular. So, for you, having the ASHP commissioned in December then I would expect quite a hit on the bill – but you may find that January and February is better, even though it may be colder.
The other thing (certainly for us) you should think about how you measure the usage. If you use the online graphs (which are currently not working for us) then it should be accurate – but if you use a magnetic electricity smart meter (the kind where you place a magnet around the feed) it won’t give reliable results and will differ significantly from the actual usage.

Mars 15 January 2021 - 11:18

Thanks for the comment and feedback Mike.

Great to “meet” someone that has the same ASHP as us. As nothing more than a personal comparison and to gauge our own efficiency, can you please give us an idea of how much space your pump is heating and what the performance of the pump has been like since we hit this cold snap in January?

Mike Hyland 22 January 2021 - 19:44

Hi Mars – The pump is trying to heat 207sqm using underfloor downstairs and rads upstairs.
The House is a mixture on new build and renovation of a very old chapel. Because we had planned, from the start, to have air source then all insulation has been up-spec’d. There are three roofs and they have been built to ‘warm roof’ standards. So, we are well insulated.

I can’t tell you figures for this Jan because the graphs have broken and I currently have no access to the figures. However, I can give you the overall usage for 2020 was 5548kWh. I haven’t worked out the cost as yet.

We’ve had the pump now three winters and it’s never been an issue actually heating the place – January last year used 827kWh.

For the whole of 2020 we’ve had four of us here – kids are adults at 25+ – and the hot water takes a serious hit with four showers a day.

SATINDER 15 February 2021 - 09:12

Are you sure Symbio are charging 10p as I am getting 14.99p from them.

Mars 15 February 2021 - 09:36

Morning. Yes our rate till the end of Feb is just under 11p. They have now hiked the price to over 15p for us so looking for a new provider.

Vince Williams 3 January 2021 - 09:44

I’m glad I came across your site, our annual graph looks almost exactly the same as yours with the large increase in energy consumption in Dec, so I was a bit worried we had a fault developing. Our annual cost this year comes out at £1250 and that’s for a standard 4 bed detached Yr 2000 on a regular housing estate, plus it includes charging our EV. No gas or oil to pay for and with Solar PV feed in tariff income to off set that expense then all is good.

Mars 3 January 2021 - 10:24

Thanks for the feedback and sharing your experience Vince. What brand ASHP are you running?

George 6 January 2021 - 12:22

Well done for moving to Symbio! I’m not sure how long they will survive offering the rates that they do but so far we haven’t had any issues using the variable direct debit and I’ve just signed up to a 12 month contract at 10.9p after trialling them for a few months on a variable contract. Most people seem to have an issue when they select the fixed yearly direct debit that isn’t adjusted each month depending on usage.

Here is our data for the year:

Month Days Day Month Heating Hot Water Total
Jan-20 31 £8.69 £269.39 1979.9 478.6 2458.5 *3 days data only
Feb-20 29 £7.91 £292.06 1623.7 469.9 2093.6
Mar-20 31 £7.20 £284.40 1529.5 509.2 2038.7
Apr-20 30 £3.57 £136.44 513.1 465 978.1
May-20 31 £2.49 £98.12 238.5 464.9 703.4
Jun-20 30 £1.66 £63.29 59.9 393.8 453.7
Jul-20 31 £1.60 £63.18 26.8 426.1 452.9
Aug-20 31 £1.48 £45.77 39.7 378.3 418
Sep-20 30 £1.98 £59.34 123.9 418 541.9
Oct-20 31 £4.11 £127.52 671.1 493.5 1164.6
Nov-20 30 £5.36 £160.72 825.7 524.9 1350.6
Dec-20 31 £7.41 £229.80 1276.2 654.9 1931.1
Total 366 £4.45 £1,830.04 Total 8908 5677.1 14585.1 kWh
Average 742.33 473.09

Its done much better than expected as we were spending a similar amount on oil heating a 4 bed detached house and since our extension its now 7 bedrooms.

The system had its first service this year for less than £200 which I thought was reasonable.

Mars 6 January 2021 - 13:06

Their rate is astonishingly low compared to everyone else in the market and I certainly hope that they survive. The switch was seamless and the response times from their support team were reasonable too. So far, so good.

Your numbers are looking good for a large house.

Are you running 24/7?

George 6 January 2021 - 13:57

I would say its not running 24/7 in the winter as every room has underfloor heating or a radiator with its own zone that calls for a heat based on room temp so I can’t force the pump to run 24/7 unless I set the rooms to a very high temp that it wont achieve.

I initially ran it on a set flow temp of 45 degrees and the costs were much higher compared to switching it to the compensation setting where it rarely flows above 40 degrees now unless its really cold. Today is 3 degrees at home and its currently flowing at 38 and returning at 34-35.

When it was serviced by a local ecodan certified installer/service centre the engineer seemed surprised it was running ok on the compensation setting as he said he always just sets it at the spec’d install temp. It would be fine if it was cold all year round but when its 10-15 degrees outside I don’t think the flow temp needs to be 45 or the heat pump shouldn’t be working so hard and consuming higher amounts of electricity.

Mars 29 January 2021 - 20:32

Not sure I’ll be sticking with Symbio very long. Just got an email from them saying they’re increasing our tariff to 16.557p per kWh, which is a staggering increase, from March 1.

Satinder 15 February 2021 - 09:43

Octopus quoted me 13p on Go daytime and others 14p but I am on Agile I would suggest looking at Octopus as you can switch every 30 days I think.

Agiles been super expensive but mostly coming down to 9p recently but still cheaper 95% than any body else
Even with the 5p 4 hour rate overnight its a saving with GO

I have done a few videos on my Agile experience.

Mars 15 February 2021 - 15:26

Thanks Satinder. Will check them out.

Mark+Crooks 3 February 2021 - 18:12

I’ve been with Utility Point for a couple of years now. They seem reasonable and I’ve never had a price increase mid term. Currently on 12.7p per kWh.

Mars 3 February 2021 - 18:13

Thanks Mark. I’ll check them out tonight.

Jon 6 February 2021 - 18:40

All been really interesting and useful information across all your ASHP articles. Looking to install one at an old house and been keen to find some real info on running costs/performance in such a property. Have you considered a battery to accompany your solar? They are also chargeable at night, with lost cost electricity. I’ve been looking at Octopus Energy for this.

Mars 6 February 2021 - 22:11

Thanks for the comments Jon, and glad you’ve found the articles helpful.

When we put the solar in we looked at batteries, but after crunching the numbers the ROI on a large battery didn’t work out. In addition to this, from autumn to late spring we’re hardly exporting any electricity because our ASHP uses it all.

The prospect of using cheap power from Octopus late at night to recharge is clever. I like that idea. We don’t have a smart metre though. Since you do, the calculations should be interesting. I believe that Tesla batteries last 10 years, so it’s a matter of seeing whether you could cram £8,000 worth electricity into it over 10 years to recoup the investment.

Do you have an ASHP?

Jon 16 February 2021 - 18:42

I get the keys to my new/old house on Friday. So am still at the number crunching stage! Which is why your articles and figures have been so helpful for me.
Probably 30% of my decision is my environmental conscious and liking the idea of being more green 🙂 I’m fairly sold on solar and a battery, as I am a low electricity user otherwise and reckon I should make money on it overall. My hesitation is, how warm I’ll keep the house economically with ASHP like last week when Norfolk hit -10! And generally how economical it will be. For me to ponder and try to gestimate!
About to watch your second winter ASHP vid and perhaps find out more! Thanks again for your great articles.


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