This seems like easily the biggest win available to most homes, at least in the UK. Modern building regulations mean that new homes have to be so well-insulate

This seems like easily the biggest win available to most homes, at least in the UK. Modern building regulations mean that new homes have to be so well-insulated that heating requirements are small. We have a lot of old housing that was not built to those regulations; some of that has been refitted with insulation, and the rest should be. Whereas the heat that goes into hot water just goes down the drain, even in the most modern homes!