So - I actually physically run 2 mining rigs - each with 6 Nvidia GTX 1070s - pulling 1020 Watts each. They each heat a room fairly nicely and I make around maybe $300 in profit from just selling coins per month. This is AFTER I subtract my electricity costs which for these 2 rigs is about $160 per month. I have not quantified the heating benefits but I'd estimate it at maybe $20 a month. I built them back in March/April for $6k total, and I've made twice that so far - paying for itself already and extra $$$ - plus I still have the hardware going or I can resell it at a profit even thanks to the shortage of high end video cards due to all these crypto miners like myself.

In the summer, I had the rigs in 1 room air cooled with just the windows open - no problems with 90 degree F days at all. Fun project, and so far quite successful.