Kansas City, Missouri. We had the Polar Vortex come thru temps[The High] were below zero for two days with 4" of snow blowing around. The girls did fine, Had 2-3 eggs from six hens a day. The coop is not heated from lamps, just the dog dish water heater and the hens body heat. The temps in the coop didn't get below 20 degrees. Which surprised me totally. They don't like the snow, but when it was sunny they played in the dirt in the covered run. I have a automatic pop door it opens and shuts at dawn and dusk. I wouldn't think about leaving them inside all day. The right breed helps, I have Orpingtons, Brahmas and Black Stars.