It would be good to get an idea from around the country on the general costs of running an air source heat pump retro fitted to an older building (around 40 years old) rather than a new purpose built house. I’m in a small, 1 bedroom cottage, probably around 80sq.m floor size with double glazing and loads of insulation. I’m in the sticks, so to speak, close to the coldest place in the UK so perhaps this is a disadvantage, I don’t know. Anyway, if I switch on my heating at 18deg the heat pump chews through 15KwH per day. If I set the thermostat to 21deg it chews through 26KwH. I find it very expensive to run in the height of winter. The pumps and system are all serviced at 12 monthly intervals and the residents of the other cottages all same the same. So it’s not mine being faulty. If during a particularly freezing winter the thermostat is turned up to 23 or 24deg then a bill for £230/mth is not uncommon. Obviously, come January, if we get a bad spell like last year, and they crank up the unit cost of electric the bill will be ridiculous to stay warm. I would love to hear from anyone else on how they find their heat pumps. p.s. In my last place which was pretty much the same size I had gas central heating and on average it cost £90/M and it was toasty toasty all day long. I had no idea about heat pumps until I moved and nobody said anything about the costs to heat these cottages until I moved in, just in time for winter to set in. Boy, did I get a shock!
Thanks, Mitch. These are the numbers the debate never gets: 15 kWh a day at 18°C, 26 at 21°C. Could you add what you pay per kWh, and the make and size of the unit? Anyone else with a heat pump in an older house, please post yours, good or bad.
Aye, last year it was around the 23/24p/Kw. I’m not sure about the Air to Water Heat Pump made by Mitsubishi it says it’s “Rated Heating Capacity” is 5kw. There’s other numbers etc but it’s all gobbledegook to me. I’m not an electrician 
Thanks, Mitch. At the 23 to 24p a unit you paid last year, 15 kWh a day at 18°C is about £3.50 a day and 26 kWh at 21°C about £6. At this winter’s average price-cap rate of 26.32p (no VAT on electricity until March), it’s about £3.95 and £6.85. The standing charge comes on top either way. That’s a 5 kW Mitsubishi air-to-water unit in a cottage of about 80 square metres. Anyone else with a heat pump in an older house, please add your figures.
Yes, Richard. It’s all to do with the outside temperature too. When it’s minus 6 or lower during the night these compressors are working overtime trying to heat the place. They’re very noisy at the dead of night, humming away continuously. Even during the day with the sun out and it is at zero degrees these comps hardly ever stopped. I should also say that it is 8 years old so not a new up to date unit. Perhaps the technology today is such that a newer compressor would different. Would be good to hear what others have to say
It faces North too so when the north wind blows etc, During the winter months it gets no exposure to the sun whatsoever. It sits at the back in the shadow of the property all day long. I suppose all these things have an effect
Thanks, Mitch. Those details matter. A heat pump takes its heat from the outside air, so the colder it gets, the harder it works and the less heat it gets for each unit of electricity, just when you need it most. Sun on the unit itself makes little difference: it’s the air temperature that counts. It would be good to hear from anyone with a newer unit in an older house, to see whether it does much better than your eight-year-old one.
There is lots of misinformation about heat pumps and how they function at different outside temperatures. I wrote an article to try to explain how they work and how outside temperatures affect them. You can read it here: Air Sourced Heat Pumps - Good For Me, But Not For Thee
Where I live on the prairies in Canada we get lots of -30C to -40C weather. Heat pumps are useless here. However, on the West Coast where winters are mild, they can provide a small savings over gas heat.
I worked for a number of years in Sakhalin Island (Russia) where we had heat pumps backed up by hydronic heating. During the summer, late spring and early fall, the heat pumps worked fairly well. But as soon as cold weather below freezing began, that was the end of heat pumps and it was the gas fired hydronic heating that kept us warm.
Thanks for that confirmation. I read your report too and it’s just as I thought with these things. Turns out that they tried ground source heat pumps but for done reason they were a complete waste of time so now it’s these things. Hey ho, if only we could have cheap energy
Oh wait this renewable stuff is cheap, we’re told. The wind and the sun is free so… Ah, as it’s turned out was was just a lie. How dare they! Eh Greta?