zlacker

> Heat pumps don’t work well on old, poorly insulated houses in cold climates. If they can keep up, which is a big if, the price of electricity generally dwarfs natural gas, even if the heat pump is running at 250-300% efficiency.

I've got a 1930s semi-detached house (UK, north of England) - heated solely by a ASHP for both heating and hot water.

Our Seasonal Coefficient of Performance is currently 3.47 (347% efficient) - even if limit that to just last month (coldest month of the winter so far in the UK) our COP was 3.25 (325% efficiency).

Roughly speaking if you can achieve a COP over 3.2x in the UK it should be roughly on a par with gas, assuming you go 'gas free' (i.e. you can make the saving on the gas standing charge).

Personally we're running at ~£200 annual saving vs. my estimate of what costs would be for equivalent gas boiler - that's thanks in part to being able to do all our hot-water heating at night rates.

House wise - we don't have cavity wall insulation, have 15+ year old double-glazing and probably should have more insulation in the loft (it fills the rafters but I think these days that's considered not enough).

Also with changes to ECO (energy company obligations) and RO (renewables obligations) the differential between gas and electric will reduce further

Anyhoo - added my example to show that ASHP can work perfectly fine in old, poorly insulated homes in (moderately) cold climates.

ECO/RO link - https://www.moneysavingexpert.com/news/2025/11/energy-bill-c...

>>footyd+(OP)
The issue with poorly insulated houses in cold climates is not about efficiency. The issue is that the thaw cycle makes it impossible to actually come up to temp because too much heat is lost during thawing. Most of the UK isn’t really considered “cold”, which is probably why you don’t have this issue.

>>hippo2+XU
Yeah the UK isn't really very 'cold', but figured would include my example to show that not a problem in UK-equivalent of cold climates.

From a quick skim around it appears ASHPs can continue to work at -20c even -30c IF they are units that were designed for cold climate operation, albeit they can't secure the same SCOP/efficiency as they can with warmer temps.

It also looks like homes in these colder areas will often install the ASHP + have some form of additional heating as a back-up (e.g. electric heating) to compensate for the limitations of the ASHP in the coldest weather.