The outside temp is 27F, the coop temp with the sensor on the roosting/nesting box where I left 3 of the 5 birds moved there tonight is....ta da......THIRTY FOUR DEGREES. I;ve had a 60W incandescent out there since we've had the electric hooked up and that's about what that bulb generated; it was higher at lower temps, lower at higher temps. We did that just to see what 60W added. Amazing how many BTUs they generate (CTUs: Chicken Thermal Units). Tucked in for the 8-16" storm moving over northern Colorado.