I think when people think warm, they think shut the house up tight and turn up the heat. We try to apply that concept to chickens and that is where I went wrong the first years. I kept thinking that I needed to block off the outdoor air, so they could be warmer.
I have now come to the idea, that a chicken can keep herself warm if she is protected from the wind and MOISTURE. A wet chicken is a cold one, a dry chicken is warm. When people talk about ventilation, it just seems so counter intuitive to keep chickens warm, you let in the cold air.
but what you are doing is letting the moisture out.
Think of being in a car with a bunch of people when it is cold out, with out circulation of air, within minutes, the moisture begins to collect. Chickens too put off a lot of moisture with their breath and feces. To keep chickens warm, they need to have space around them, they need to be away from the wall, and away from the ceiling where their moisture will collect. Dry absorbing bedding down below. Don't look at your door, look at where your roosts are, and how close to the ceiling or wall your chickens are when they are on them.
Mrs K