thank you so much! a hot spot is a much better idea!Might help if you post some pictures of the coop are at least sizes. I don't think I would really try to heat the whole coop but rather give them a spot within the coop to go warm up if needed. Maybe a couple heating pads under a piece of plywood or something else to cover and protect the heating pad. These heating pads stay on all the time, (some heating pads turn off after a set amount of time).
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Or a the Cozy Flat panel heater.
Many options out there some more risky than others.
If you go heat lamp try the Prima one with a quality heavy duty heat buld or shatterproof ones.Like this.
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The one pictured is from QC Supply
Infrared Heavy-Duty Hard Glass Heat Bulbs - 175 Watt - Red Glass
Buy backups also!