I read articles on coop design and they all mention having vents is very important in the winter to prevent frost bite and for, well, venting. They all are kinda vague and dont give any size recommendations. My coop has a 4x6 foot section and a 8x8 ft section (new addition) which are connected. How big should the vents be? I live in North East Wisconsin so I want to have proper ventilation but dont want them to be too big and have a lot of cold air enter the coop. Thanks for your help!