Hiya, and welcome to BYC!! 
Temp is what causes frostbite, and humidity is the catalyst. We've dealt with it having no open water in the coop (nipple bucket) horse bedding pellets on the floor (keep coop dry) stall refresher on top of the nests where they perch, and a radiant heater that keeps the coop above freezing.
If you're still having issues with chickens with frostbite, this is a great article. https://www.backyardchickens.com/ar...to-know-about-injury-care-and-recovery.78168/

Temp is what causes frostbite, and humidity is the catalyst. We've dealt with it having no open water in the coop (nipple bucket) horse bedding pellets on the floor (keep coop dry) stall refresher on top of the nests where they perch, and a radiant heater that keeps the coop above freezing.
If you're still having issues with chickens with frostbite, this is a great article. https://www.backyardchickens.com/ar...to-know-about-injury-care-and-recovery.78168/