Stop heating your coop. Do you have good ventilation. Chickens temp runs at 106F, They roost and cover up their feet. They grow a down coat. Just like some dogs they have two coats, their down one and their feathers. They snuggle together when it gets colder. If you start heating their coop as soon as it get cold ( to YOU) they won't grow their down coat. Chickens don't sweat, so they can't get rid of the excess heat your are providing. With heat and inadequate venting humidity builds up and the combs and birds get cold/wet
and hence frostbite. Keep your chickens DRY and they will be fine. Wash your hands but dry only one. Go outside when it's really cold and see how that wet hand feels.
If you have started heating already you might have to continue for this winter. But 0 F is nothing to chickens. What do you suppose the blue jays, the crows, the robins do in the winter. Not to mention the chick-a-dees we have here in Maine in the winter.
I kept 4 birds in an uninsulated coop without heat in the winter of '18-19 with temps -20- -30 and they were fine. Actually laid an egg every day that winter. Without a light even.