My understanding (and I'd love to be wrong here because it annoys me that I can't take advantage of high efficiency systems) is that: 1. Existing UK homes use

My understanding (and I'd love to be wrong here because it annoys me that I can't take advantage of high efficiency systems) is that: 1. Existing UK homes use radiators that would need to be replaced with larger radiators with an air-to-water heat pump, due to the water not being as hot as a traditional radiator system. Some of this is cost (replacing radiators), some of this is simply not having the space - many radiators are installed below windows so there isn't much scope to increase their size 2. Replacing radiators with an air-to-air system in each room is too expensive (especially since older homes often use solid brick/concrete for internal walls), as well as a large number of terraced houses with limited space for external piping/units. 3. Our mild climate (as well as housing stock age -- and, I'm betting, good historical access to local fossil fuels) means UK homes are very poorly insulated, and with our humid climate can have humidity + mould issues if retrofitted with insulation that reduces drafts.