Good thing, this message came to my inbox. I just built a new movable chicken coop, and I did not put any ventilation holes in the night box or laying boxes. I live in S. Ontario and figured the cracks and pophole would be sufficient. As the cold weather approaches, I anticipate they will spend more time inside the night box. I am going out to rectify this at once. Thanks for the very well written article and the excellent explanation of the types of ventilation.