I asked the same thing! I'm new to this and had no idea. They were almost a month old (last umm Friday I think it was). The hens were mostly feathered out, but the roo's were still fluff on the backs & chest. Everyone said they would be fine with a lamp. I used a 150 watt, about 2 feet from the ground. A week later and they are all doing great! It got down to 39 (cold for south Louisiana). If it's above freezing I'd go for it.