Also, find out the heating effiency between each unit. Measure how many degrees each unit raiaes the temperature compared to how much electricity it eats. (if heater is using another fuel also, like gas, factor that in). Basically: how many degrees per dollar or whatever unit of fiat you use locally. I know electric heaters are 100% percentbefficient (yes really). Idk about the BTC miners. I would imagine it's not 100% bc some energy is used for the calculations, but the diff might be megligible.

So thing to consider: price of units, longevity of units, how much actual heat you'll get per $ of fuel/electricity. And after that seebif it all would be worth it: as in will you still runa good chance of spending less $ to mine a bitcoin than you would just buying it outright at an average pricenof it nowdays (you could also try average forecasted price for however long you think it'll take you to mine one, but thats iffy because there's a netural tendency to be optimistic about the future price of something you have an emotional investment in). Then there's one-time setupncosts.

Also, you may want to think about the non monetary costs of the set up: convenience. Where are the units going to be? Are they going to get in the way? Will they be loud and annoying? Etc.