I have 4 hens that are 6 months old. My coop is a 8 X 10 shed with insulation in the walls and roof. I am using the deep litter method to keep the floor warm. They are out of drafts and the coop is not damp. We live in New Hampshire and I am wondering what temperature is too cold for a chicken? At what temp should I add a heat light or small heater? Thanks in advance.