Chris

I did extensive research into heat pumps before eventually installing a wood pellet biomass system because the heat loss at my old house was awful and remedying it was non-trivial due to its construction. At the time I was looking at ground source with a borehole and sealed loop collectors due to lack of available land for trenched ground loop collectors and the relatively poor efficiency of air source heat pumps at the time.

However, that was 15 years ago and in that time, air source heat pumps have become as efficient as ground source pumps were back then. So I’m guessing what I learned then pertains to what you need to do now, which is get a surveyor out who is qualified to do a full heat loss survey on your house (ideally the one where they tape up your front door with plastic sheeting and blow warm air into the property). Find out exactly what the heat requirement for your house is, then get a heat pump installer to specify and cost quote a system for you based on that precise requirement.

Discuss with them whether you’re sticking with radiators, and how much larger the panels will need to be in each room (if at all - if your rads are very old, simply replacing them with super-modern efficient ones *might* be enough). Consider whether you’d like to switch to underfloor heating, downstairs at least. This is the most efficient way to heat a home and is ideally suited to the lower heat output of a heat pump.

As I said, all of this research led us not to go ahead with it, as we learned our house was particularly ill suited. So I can’t advise you on what actually happens when you put one in. But it is definitely worth doing the research.