Yes it will be slow, even more so while it's still possible and cheaper just to replace a gas boiler like for like . People don't buy new heating systems like new cars, they buy one when the old one is bust or too expensive to run. Since most are on gas, which costs about the same per kWh of heat for now, much easier just to chuck a new gas boiler in and a lot cheaper and quicker. We only did HP because we were building the house.
That's before considering the rest of the system. You can't just hang a heat pump on to a wet system with radiators sized for 65 degree C water flow, so you need to fit bigger rads. And microbore piping will need replacing. And heat pumps cost more, and the installation certainly does. You're not going to want to start on all that when your heating breaks down in January.
There's also a lot of bad stories around about heat pumps not getting the house warm enough or using too much electricity.
FWIW, our air source heat pump (ASHP) consumed about 3700kWh for heating and hot water from Apr 22 to Mar 23. That's for a 212 sq. metre heated space with a B energy rating. (the heat pump has its own meter, although I'm pretty sure the pumps aren't on it, so they might use maybe 300kWh a year?).
Insulation is important whatever your heating source. our ASHP is rated at 11.2kW (output). We could probably have got away with 8kW but it was a bit marginal. Most builders/plumbers will just throw in a 30kW gas boiler for the average house without doing any sort of heat loss calculation. That's one of the reasons that gas CH tends to be a lot more responsive, it typically has a much bigger margin to heat the house up quickly as well as replacing the ongoing heat loss. I think this probably accounts for some of the stories of heat pumps just not warming the house enough. If we turn the heating off when we go away in cold weather, it could take 24 hours to get the house warm again when we get home. (it doesn't help in that respect that we have underfloor heating which has a big lag) We just run it 24/7 except for 3-4 months in the summer when the house is more likely to be over warm just through solar gain.
Last edited by: Manatee on Sat 15 Apr 23 at 11:11
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