I'm building a insulated 8x8 coop that will be air tight when I'm done so I know that I need to have ventilation for the girls in the winter but I'm confused about how much they need vs. Drafty. We are only talking winter (-10 @ worst ) in the summer it will be opened up. I am a hvac guy so normaly I have a % for this. I never thought chicken coops would require so much thought! I don't mind natural or forced ventilation ideas.