Let them choose. I would shut the pop up door at - 25 F. Seriously if they can get into shelter, they will if the need too. Last year I was watching mine, it was -19, but the sun was shining. I saw a ball of ice on the foot of one of my birds, she kind of limped. I watched carefully, she held her foot up close to her, and it melted immediately. Chickens produce a lot of heat.
Mine have shelters, for wind breaks, and they like fresh air.
Mine have shelters, for wind breaks, and they like fresh air.
