If the existing A/C don’t support heating, then presumably heat pumps are displacing far inferior gas or resistive electric units (or even wood burning heaters). Heat pumps absolutely destroy them in terms of efficiency, and it’s hard to believe the embodied emissions plus ongoing emissions would be worse with a heat pump. And just as importantly, the fossil fuel industry needs to be made unprofitable as soon as possible, and anything that gets people off gas is therefore a good thing.