A few weeks ago, I posted that we’d finally ripped out the old gas boiler and gone all-in on an air-source heat pump. Well, the UK has gifted us its traditional “wet sunshine” autumn, so I thought I’d share some real-world numbers now we’ve had it running from 12th October to 1st December 2025.
Sorry in advance – there are numbers and a bit of jargon ahead.
The headline stats (12 Oct → 1 Dec)
Total output from the heat pump
- 2,080 kWh delivered to the house
- 223 kWh hot water
- 1,857 kWh space heating
Electricity used (input)
- 520 kWh total
- 97 kWh for water
- 423 kWh for heating
That gives an average system COP of exactly 4.0 over the whole period (2,080 ÷ 520). And all for a total cost of £36.40, we are pretty happy with that for the first seven weeks, especially as it includes hot water.
Worst single day so far (a properly chilly one) was about 25 kWh of electricity for whole-house heating, and the house still sat at a rock-steady 21 °C. We both work from home now, so the heating basically never goes off – a very different pattern from when we commuted, and the house was empty all day.
The money bit
Everything so far has been shifted onto our EV overnight tariff + home batteries, effectively ~7 p/kWh.
(Yes, I know that won’t be 100 % possible in the depths of January/February – I’m budgeting maybe 10 % of winter use at peak rate (~29 p/kWh) because we have a very EV-friendly tariff.)
For comparison:
– Old gas boiler: ~12,000 kWh/year when we actually used the heating properly
– Gas unit rate right now: ~5.5 p/kWh + standing charge
Even if we end up paying an effective 10-12 p/kWh average across the whole year for the electricity, we’ll still come out ahead on running costs – and that’s before the zero carbon part.
The takeaway
If you have:
– a reasonably well-insulated house (ours is a 1980s Detached, cavity walls filled, loft done, double glazing, no heroic draughts)
– the ability to access a cheap off-peak tariff (EV tariff, battery, or one of the dedicated heat-pump tariffs now appearing)
…then it’s a no-brainer for us.
If your house is draughty and poorly insulated? Honestly, fix the fabric first. A heat pump in a sieve will still be expensive to run.
I’ll do another update once we’ve had a proper cold snap. So far, though, very, very pleased we took the plunge.
(And yes, the house is quieter, the boiler does not wake us up in the night, and we have hot water that recovers crazy-fast. Little wins.)
Trevor
1st December 2025