I can attest, I have a 9 card mining setup which pulls around 330w per card 24/7. In the summer when it was 70-80 degrees outside it was enough to keep a large basement in the 90s, plus the rest of the house uncomfortably warm. I had to purchase an AC to keep the place livable.

Now that winter is coming around I look forward to the extra heating.

There seems to be discussion in these comments about mining for the purpose of heating a home, but the heating is a bonus. You're making money AND saving on energy, that's the important part.

Plus, in my opinion, a constant heat source like a mining rig is preferable to an older cycling central system which can be slightly disturbing as it loudly cycles on and off throughout the day...