I dare say that in many situations, an aircon running on heating would be a better heater than an old miner, because of typical COP, eg. using 1000 watts to do the same amount of heating as a 3000w fan heater / oil heater / miner. Not to mention floor space usage / noise.
Eg. a miner that's 96 TH/s, 2400 watts, 1.5% pool fee, would lose about $3.14/day @ $0.15/kwh power cost, compared to a small aircon using say 800 watts to pump 2400 watts running 24/7 would cost about $2.88/day (of course if your aircon never stops running, it's undersized.)
Modest/excess wattage spent on lotto mining sounds good.
Depends on the use case. I am sitting in the back room of my condo with a 1 board S9 at the moment keeping the temp here above 72f [22c] BUT since I have 1 zone heat I get to keep the rest of the place at 66f [19c] I just have 1 zone heat / aircon for here so although a lot less efficient, it is cheaper to run.
In the bedroom I have a 2 board 400w give or take L3 running on a LTC / Doge lotto pool. So far got a few doge blocks over the last couple of winters. But when I am sleeping I am not heating the rest of the place.
I rotate through old miners depending on what is working and if I have sold any over time.
-Dave
How much BTC are you making per one week of leaving it on? What pool do you use?