Inside my coop got down to -14 on Saturday. No heat, no insulation, lots of ventilation, wind/drafts blocked. All 5 were just fine...eating, drinking (warm water I brought in,) pooping, scratching. I would probably worry at -25 & -30, like some of our fellow BYC-ers in the midwest, but here in Maine--comparatively speaking--it's been reasonable.So my inside coop temperature is 10F. I chose not to put a heat lamp in the coop, but now I am a little nervous. My hubby keeps telling me we should have put a heat lamp in there. I know that many of you have temperatures much lower.... Please tell me that my chickens are going to be fine.... I added 2 extra bags of leaves, covered some lower vents, fed some warm oatmeal right before roosting, as well as a little extra scratch. My coop is 5x8, with 2 small triangle vents on each end ( I covered the lower ones) and then one vent on the back side that is open all the time, and a window on the front that is currently closed. I didn't feel any drafts when I climbed in there to check.