Hate to break the bubble, but I don't think you need a heat lamp by the way you describe things. What is your general location? Second question, and it is somewhat important, "what kind of chickens do you have???"
You can see my location, it is in my profile. I'm in Zone 5. I have Bantam Serama chickens besides my other LF chickens. They are somewhat not very cold hardy breed. I winter over the whole pet flock in my Garage loft. I only provide
some heat if the temps get
VERY LOW, like 0°F or colder outdoors. I only Heat to have in-garage temps to just above freezing then.
The problem with adding heat to a coop are these.::
Chickens do not grow/develop as much deep down feathers like they normally would.
Chickens get used to the heated area, and if you have a power failure, your chicken are in trouble then.
If you do live in an extreme cold climate, then some additional heat is needed. Usually during night time,
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,and
