[joaodlf]

Heat pumps take much longer to heat the system, to get it to the desired temperature. Combine that with a property that is not insulated to very high standard, and you get a heating system that is incapable of keeping you warm.

Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.

[blitzar]

Speed / response is a perfectly valid difference. Had not considered it.

Leaky houses are already throwing money at the heating problem, and perhaps with a slower response time you would 'idle' the heating circuit at a passive 25C against 18C room temperature, and throttling up from there. Throwing money at it works!