Not really, of course it depends, but IF the actual heat diffusion system is compatible (fan-coils or under floor) it can be pretty much "swap one unit with ano

Not really, of course it depends, but IF the actual heat diffusion system is compatible (fan-coils or under floor) it can be pretty much "swap one unit with another", at least for single units. Still, to give you a single datapoint, I just replaced on a unit a small gas heater with a heat pump and it was really a "swap one unit with the other", still a few issues came out: 1) the cost of the unit, even considering that it doubles as air conditioning/refreshing was only affordable because of some government subsidies (think of 6-7,000 Euro compared to 2,000 Euro for a gas heater and 2,500 Euro for a more traditional conditioning unit) 2) for some reasons, the heat pump is much slower in heating, the net result (in my specific case) is that the unit needs to be kept slightly heated on weekends (it is a small shop that closes saturday and sunday) otherwise when it opens on monday it will take forever to reach a suitable temperature. Besides, from an infrastructure point of view, if many people change from gas to electrical (though gas powered heat pumps do exist, BTW) the local increase of consumption from the grid needs to be taken into account.