I live in one of the coldest parts of Colorado, -30* is common in the winter, my coop is NOT heated, and I have never lost a chicken. They decide when to come out, I always open the run up and the choose to free range in snow, rain or wind. If it is too cold or wet, they decide if they want out or not. They love it after a rain, the other poster is correct, it brings up all the worms and bugs, they are in chicken heaven!