I did the same. Locked the coop up tight and put in a heat lamp. Every year I had unhealthy chickens by spring. Frostbite and respiratory issues were the biggest problems. When I quit trying to keep them warm and started keeping them dry, my flock has been much healthier.The biggest problem with adding heat, is the tendency to try and keep the heat in the coop. People tend to close up the coop to keep it warm. I did myself in the beginning. It just seemed so cold.
Chickens NEED that ventilation much more than they need the heat. They need a place to get rid of the moisture in the coop. It is much, much more important to keep chickens dry and out of the wind, than it is to keep them warm. Until I quit trying to keep chickens warm, and started keeping chickens dry, they suffered some frostbite.
Mrs K
It is currently 20* here with a light breeze. I have 9 half-naked chickens running around because they’re molting. They are outside, hunting and pecking and doing chickeny things just like always. They were fine. Seriously - this is bothering you far more than it is your chickens.I wouldn't feel as if I had to if it weren't raining. If we open up the coop then they get wet, but if we don't then they get upset. With that, we have a hen who is still molting, and she has looked pitiful all day. I just want to give them some heat to get them through the night, I won't leave it on all night either.
How is your coop set up that they get wet inside when you open it up? Pics and measurements of your coop could help us help you create a nice dry environment for them so they can be comfortable this winter.