I use a K and H heating pad that is fireproof and velcro to back or side of wall of coop near roosting area for anything below 30 degrees which is freezing. I use industrial Velcro. This way removable in the spring. Frostbite is a risk for anything below 30 degrees. I have a roof over coop/run. I tarp the whole house and put plastic over all windows with packing tape. I use a heated waterer or base for it. I use straw in run and coop to keep feet off ice and snow. I put curtains around windows inside for draft protection as well. I have one top vent open in coop and monitor wirelessly temp and humidity. When humidity up and below freezing frostbite sets in. Parts most at risk are combs, wattles, legs, feet, and toes. Can apply Vaseline to large combs/wattles to protect as well.