Air Source Heat Pump: when temperatures start to drop

by Mars
radiator with smart TRV

My personal threshold for when ambient outdoor temperatures start to go cold is 11C. Over the course of its first six months our air source heat pump has not had to work very hard. As we hit October, the average temperature has dropped to around 11C and it’s a good time to evaluate how the pump is performing.

Looking at the numbers from our metres over the past 24 hours, which has been cold and wet, we can start etching a good performance picture. We produced 80kW worth of heat using 30kW of electricity: a 2.66 coefficient of performance.

Our total electricity consumption for the 24 hours was 39kW, and we generated 8.3kW worth of solar polar.

As an average, that means we’ll be in the region of consuming 900kW worth of electricity for heating in October, which equates to roughly £130 for heating. This time last year, we got through about £250 worth of diesel, so year-on-year, we’ve registered our first saving.

More importantly than the saving itself, we are running our property much warmer than we were on oil. So, when we had the oil boiler working, we were heating the bedrooms at night, living area during the day and TV room in the evenings. Now, with the air source heating and the assortment of smart TRVs and thermostats, the house is being heated 24/7 to a set temperature in every room throughout the house with no portion of the house dropping below 19C.

Essentially, we are now paying less for heating, and heating more of the house more of the time, which is great and works for us.

As with this entire process, we will continue to monitor our heating performance. At this stage, we have no intention of changing our heating schedules, so it’ll be very interesting to see if we start to require a lot more electricity to heat the house in December and January when we approach the 0C mark.

Air source heat pump offer

If you’re interested in an air source heat pump from Global Energy Systems, you can use this code when you contact them and you’ll get £200 off your installation: GESRFAF000160


Gerald Bruce 25 January 2021 - 21:24

How have you found the winter months to be as far as cost and warth is concerned?

Mars 25 January 2021 - 22:10

In all honesty, it’s been a mixed bag of late. The house has remained warm, but the electricity consumption has been high. I’m working on a post that will showcase the pump’s performance after experiencing our first real sub-zero cold spell.

Iain Carpenter 31 January 2021 - 21:24

I’ll be v interested to read that. We are thinking about going with GlobalEnergySystems. How has the online monitoring been? Still give them a big thumbs up?

Mars 31 January 2021 - 21:49

The online monitoring has been excellent. They also tweak any number of things, and they picked up that one of the probes had failed and arranged to send someone out to replace it. So it’s been very good.

The online portal is also very good. It had a few teething issues, but this past year it’s worked well.

Mars 31 January 2021 - 21:52

If you do commit to going with them, you can use this code when you contact them and you’ll get £200 off your installation (and we’ll get some Amazon vouchers): GESRFAF000160

Steven Martin 26 April 2021 - 17:03

Hello, some useful articles here, thanks, we are considering an ASHP but have a 200 year old poorly insulated cottage. I see you are in an old property. Do you have solid stone still or have you fully insulated before installing the ASHP ? thanks

Mars 28 April 2021 - 14:52

Hi Steve. We are a brick farmhouse, but the full inner walls (cavity space) have been insulated.

David Willetts 11 October 2021 - 15:52

Hi Steve. We have double brick walls with out a gap so cannot insulate them. We had a ASHP fitted in January 2021 and after teething problems found if very effective. When the installers came they measure each room to ascertain which heat pump is needed. Hope this helps

Michael Stewart 13 April 2021 - 17:38

Hi, did you manage to create a new post on the colder months, we are also looking to go with GES and wondering how it was fairing. Out of curiosity how many sqm is your house? Many thanks

Mars 17 April 2021 - 17:39

Hi Michael. Here’s a very recent update (, but we have got a significant performance update coming out next week, and GES have been excellent in their support throughout. The next update will be very interesting for all people with ASHPs.

We’re heating around 4,000 sqft.


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