I've never put much thought into this but my mother who spent some of her teenage years in the UK in the 70's used to use a hot water bottle. Here in the US, we

I've never put much thought into this but my mother who spent some of her teenage years in the UK in the 70's used to use a hot water bottle. Here in the US, we had a mid-century ideal of "energy too cheap to meter" that would have been provided by the burgeoning nuclear industry. It never really panned out, but a lot of houses had things like radiant heaters in floors and room wrapping baseboard heaters installed for comfort which is nicer than having to deal with a fluid filled bladder, but obviously much more costly.