A coworker of mine mines ETH to heat his house and I am considering that too. I am not sure how much you can save money compared to electric heating when you account for the cost of GPUs, though.

Heat pumps have better energy efficiency than electric heaters but whether that translates to cheaper costs is another thing. Heat pumps are expensive (about $3000 per pump) and they require regular maintenance (a few hundred bucks per pump every few years). They're also big, bulky and noisy and installation requires poking holes in exterior walls.

I have 3 heat pumps and 2 fire places in my house but I still do need a bunch of electric heaters when it gets properly cold. The weather around here is right about freezing this time of year and so far no electric heaters are needed.

But soon it's time to turn on the heat and it's a consideration of money, not energy efficiency.