Air source heat pump consumption over summer

by Mars

We have received several questions lately about our air source heat pump consumption over summer so we pulled the data to answer this question.

From May 1, 2020, to September 1, 2020 (four months) our air source heat pump generated 2,881kW of heat using 1,084kWh of power. These figures are based on readings generated by metres that we use to get RHI payments.

We get additional data from Global Energy Systems (the manufacturers of our pump), but they have removed the breakdown for hot water demand and central heating on their new portal, so we can’t be more specific on this subject.

The data in the table below is taken from the Global Energy Systems portal and shows total consumption for the year to date, giving an indication of how often the booster (oil boiler in our case) kicked in. Over summer this typically occurs to get flow rate up when the pump has been dormant for prolonged periods of time; over winter, when the pump is running 24/7, this usually occurs to defrost and de-ice the pump.

air source heat pump consumption over summer

You can ignore the room temperature column above as that takes readings in our utility room and provides no useful insights. I also have no clue as to why the recorded average temperature in May was registered at 9C because our utility room is always extremely warm. Odd, but not relevant.

The ambient temperature column, however, is interesting as that provides the mean outdoor temperature for that month. You can see that September is a lot cooler than August (about 3C cooler) and the ASHP consumption is nearly double.

Using the data provided above, it’s now simple to apply your kWh electricity tariff from your provider to work out how much the heating would cost to run.

Apart from May, it’s been a cloudy, rainy summer with above average ambient outdoor temperatures for our area. Having said that, there were times over August and September where nighttime temperatures were cold and the heating did kick in, and that’s reflected in the table above.

What may also be useful to note is that we typically have our showers in the morning, so on sunny, light days our hot water is heated using electricity produced by our solar panel array, and over summer and autumn months the solar system goes a long way to driving the electricity demand for the air source heat pump during daylight hours.

We heat our water to 42C using the ASHP, but it does heat to 60C using surplus solar production from our iBoost that we had installed. Our central heating flow temperature is set to 45C.

In closing, even though we no longer have the data split from Global Energy Systems for heating and hot water, I was able to find a graph from last year’s data (taken from their old portal) which shows that over summer (July and August) the bulk of the ASHP’s activity is centered around generating hot water.

We hope that this gives you some insights into our air source heat pump consumption over summer. Feedback and questions welcome. Please leave comments below.


Steffan 2 October 2020 - 12:34

So the summer months (average outdoor temp above 10C) you have a heat pump COP of 2881/1084 = 2.7 which isn’t bad at all. Winter could be the same, but maybe worse, for performance.

If we assume as a household you use 2100KWh of hot water a year, thats about 700KWh of hot water over four months. In that four months you’ve used 2880 KWh of heat, so that means 2100KWh of heating in the summer (plus the 700KWh of hot water assuming you are typical users).

From the bottom graph it doesn’t seem like your internal temp is that high, probably set around 20C which is very modest, but the heating requirement is very sensitive to temperature. This suggests a pretty leaky house…maybe there is something you can do turn that down but who knows (your house looks very nice by the way ;-).

My opinion on the heat pump experiment is that you would help it out a lot if you could somehow trim that heat loss. As it is I wonder that even at 18KW that it’s enough for your house…

Mars 2 October 2020 - 21:41

Thanks for the feedback, analysis and comments Stefan.

Regarding the internal temperature, I mentioned in the post that the number in the table is for our utility room and isn’t noteworthy. We heat our house to 21C throughout, and we find it a good temperature. Our TV room goes up to 23C from 17:00-22:00, and various other rooms are also increased to 23C at various times throughout the day and night.

We have worked hard on cutting out heat loss over the past 12 months, and we’ve succeeded in some areas, while others still need work, but we are getting there. This winter will be telling and will be a good data point to compare to last year.

Joe Carr 30 October 2020 - 10:17


I was wondering what your power use looked like over a day during the the winter months? The reason I ask is that we are considering an ASHP with Octopus Agile. They offer a lower tariff most of the day, but a high tariff from 4-7pm. I was wondering if this might be really advantageous. We have a large house so would be probably using a 12 or 14kW heat pump. Also we have 8.4kW of solar PV, so this may have a massive effect on grid energy bought and we wouldnt really expect to buy anything in the summer months.

Mars 30 October 2020 - 21:05

Thank you for your question Joe.

We are in the process of working on a blog piece that covers that very question, and we will provide a detailed breakdown of our consumption during October, which has had cold days and evenings, and hasn’t been great for solar production. I think the post will be ready early next week, and should go a long way to showing the hourly consumption on the coldest days and evenings.

Mars 2 November 2020 - 08:21

As promised Joe, here’s the new piece that hopefully provides you with the insights you were after:

Joe Carr 2 November 2020 - 09:07

amazing, thank you. I’ll give it a read!

Imogen 20 April 2021 - 16:56

Hi Mars, thanks for sharing these summer usage details. I was wondering if you noticed whether the decreased demand in summer has an effect on the noise of the pump outside?

I’m trying to check an assumption that these will be quieter to run when not much heating required, and mainly used for hot water. For us this will be key to whether we can install one in our small back garden.

I’m getting a lot from your posts and videos, thanks!

Mars 20 April 2021 - 22:00

Good evening. Yes, when heating demand is low, our fan slows down considerably and is much quieter. I would assume other heat pumps will do the same. As a guess, the sound level drops by about 40-50%.

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

Imogen 21 April 2021 - 13:10

Hi Mars, that description is really useful, thanks. Perhaps the sort of noise we could expect won’t be a nuisance when folks are more likely to be out in the garden. I’m still unsure – so have followed your link and reposted at the main forum.

Pauline 27 September 2021 - 09:28

I never require heating in the summer and only use hot water in the shower at most twice a day. My electricity consumption is relatively high compared to friends who have have either gas boilers or immersion heaters in there much larger houses. I have an air source heat pump, with an immersion heater if necessary, solar panels and a well insulated house. In previous properties my energy bills have never been so high. Should I turn off the heat pump altogether as it seems to consume unnecessary energy?


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