I do have a heater in the greenhouse and the comforters on the roof. They probably will help retain some of the day heat, but the GH won't get warmer than what it is when the blankets go on without a heater inside. I used a propane heater before I got electricity to the GH.
On sunny days, the GH heats up a lot even when it is cold (below freezing) outside. One of the roof window/vents has an auto vent mechanism which is handy.
The heater maintained a temp of 11.6ºC=53ºF last night. I am very glad that I put the blankets on the roof. This was one of the coldest nights since I started up the greenhouse and the next few days will have cold nights.
