So when it gets real cold watch for frost on your walls. If you see it you don't have enough ventilation. Some people think they have enough but don't really. Let Mother Nature help you. And I keep a plastic gallon jug ( Arizona Ice Tea) and if it's frozen in the morning I know it was cold...
Where are you located. You can go back to your profile and put in the state or country you live in. Help us help you. Do you have good ventilation in your coop. Dry chickens are warm chickens.