Heat pumps might work in theory but so do a lot of things, I've yet to see one that works at all without costing the owner an absolute fortune in electric.
There was an estate near to me called the Stamford Brook estate in Altrincham that was supposedly the next big thing in cheap heating using these things, it turned out so bad it made it all the way to parliament. People that rented were just upping sticks and leaving after a couple of months of electric bills, it was cheaper for them to pay the outstanding rent that it was the electric bill.
Then there is my plumber mate, he wants to get into installing heat pumps so made his own home the "show" job you need to provide. Massive extension all done to the latest regs with UFH and insulation everywhere, the rest of the house brought up to latest regs, new windows, insulation etc. The most sophisticated heat pump set up I've ever seen yet still he has to constantly put the immersion on to get anywhere near a suitable temperature needed.
He should have asked me for advice - if you are using the air from outside to heat your home, if its cold outside then its going to be cold inside, shouldn't take a genius to work that one out.