Im heating my garage and house here in Finland. Last winter there were -30C outside so two S5 kept place around +10 degree. There is no problem if miners are running and ambient temp goes down like to -20C for a while like when you opening garage door but you can't start cold miner. So you have to heat them first so basicly those are just like a cars And dont keep them too long in place where is minus degrees because the chips starting to get some ice and after that you get some problems.