Well that's easy: a 2kW Bitcoin miner heats your house just as well as a 2kW electric furnace.

(I'm kidding but I'm also not; I'm regularly amazed by the fact that the most complex and intricate computational machines have exactly the same 'output' as the most basic 'heat this piece of metal' contraptions, when looked at as a blackbox.)

While resistive heating was state of the art for years, and you might as well do some computation with the electricity before turning into heat, we can now make systems that are far more efficient ("200%" and up) by moving heat instead of generating it: https://en.wikipedia.org/wiki/Heat_pump

Have you heard of heatpumps?

Why do I suddenly hear some familiar jazz?

I definitely have, and I wouldn't use an electric furnace nowadays unless there was no alternative. That's what the 'I'm kidding' was meant for. Sadly, heat pumps can't mine Bitcoins on the side afaik, so I couldn't use those for the analogy :P

https://bitcoinminingheater.com/ is a thing. It even has a built-in thermostat to regulate its mining output to your desired temperature.