I have a winter cabin up in the mountains near Seattle, which so happens to have some of the cheapest electricity in the world. (there are quite a few cryptocurrency mines nearby) Though we generally heat the place using a modern, efficient wood stove, I've half seriously been pondering buying a few graphics cards and doing some Ethereum mining to heat the basement. If I wasn't a bit scared about it setting the place on fire I'd probably do it, but pretty sure I'd end up heating the place for free after a season.