I have a large coop for about 50 adult chickens, about 4-5 roosters, the rest hens, all standard size. Their coop is not enclosed on all 4 sides, just 3 rooms with roosts and nests, each about 9'X10' and all completely open on one side. The free-ranging space is enclosed with a high fence to keep predators out. I use a 250-watt heat lamp in each separate room in the winter, when it's down into the 20s and 30s. They seem to be fine, but I'm not sure if the light from the red lamps interferes w/ their sleep. If I go out there at night, they seem to be awake, not sleeping like on summer nights. Some of our chickens roost in the trees, don't even go into the coop at night, and they have not frozen yet.