Did a vent test today as I just finished insulating and paneling the coop. The panelling was 9 bucks a sheet. Needed three. Well I took some pine incense and put it in the coop. I shut down all the airflow and looked for smoke at the peak. There was some, then gradually I opened some vents and the smoke came billowing out. These vents were 3" circles cut in the rear doors and then I screwed some covers over them that can be adjusted as a BBQ grill would! The area at the peak is the vent, works quite well.