My zone changed recently to 7b [i'm on Long Island]. I have a 200sq/ft shed with 15x7 old Everlite greenhouse. It's my first season so it's still a work in progress. Like Ursula said the shed acts like a temp buffer for the GH. I keep tropical plants and tropical fish in a pond. In Nov i had a Diakin 24k mini split heater/AC unit installed. I have it set for 64 degrees and it seems to keep the shed at that with the GH a few degrees cooler. My first elect bill was about $60 more than usual. I'm not sure if that's an entire month. I also run a small wood burning stove to offset costs. The GH is very leek [air and water] due to a poor install, but my main issue is single pain glass has an R value less than 1. If costs get too high i'll try to figure out a way to better insulate. During the day it's fine [in the winter], it was about 40 deg outside and 80 in the GH. Then i'll have the opposite problem in the summer.
