I did a winter grow in the GH last year and it was successful...however, the insulated space I used inside the GH was only 2x4' and I wanted to grow more, so I went into a 4x4' for this winter. Last winter I was always worried about power failures because the COBS were my only heat source and if the power went off the plants would be toast (it could get down to 25F in the GH)...this winter I opted to grow in our summer rental cottage which effectively has a root cellar...ambient temps average 50-60F and the tent (with heat mats and lights) averages 50-80F...but, if the power goes out (as it did Monday) then the plants really won't notice the temp difference. I'll be back in the GH end of April....So you don't use the greenhouse in the winter? I'm jealous and would really like a greenhouse one day!