It's pretty brilliant actually. Case 1 electric space heaters blindly pass electricity through dumb wires. Case 2 instead of dumb wires you use ASICs. Case 2 is a win win that helps secure a decentralized monetary asset, get paid for it, and heat your home which you would have done anyway, all with the exact same carbon footprint (assuming you're expending equivalent amount of electricity to just heat your home as originally planned). You've basically turned PoW into proof of heating where the miner gets paid and gets the benefit of heating his home on top. And incremental environmental impact is exactly 0.
edit: quick google -> and here it is :)
https://bitcoinminingheater.com