Hey badzad, we're in for some cold again. Does your green house hold up in the 20-40 range ok?
Where I'm at we always have temps lower than forecasted. Like this morning at my place we had 28* and the last real cold spell I got a pic of my thermometer at 10.
I don't really heat in there yet, maybe a Dutch oven full of hot coals, but I keep water jugs and rocks in there for thermal mass. Once my girls actually go in the greenhouse(only cactus and succulents right now) I'll definitely be devising a good method to heat in there. Anyway, just a headsup in case ...