Hi! This is my first go at chicken keeping, I live in upstate NY where the nights are starting to get chilly. Currently, my ladies have a big front wire-encased window on the front of their house. I keep it open at night for ventilation. It was 38 degrees here last night, tonight there is a frost warning. How cold does it get before I start shutting the window? No insulation otherwise on the shed and it is raised 3 feet off the ground.