Our chicks are outside in a partitioned off chicken coop. I have a heat lamp in there, but during the day we shut it off because it gets pretty warm. We turn it back on at dusk but if it gets too warm I turn it off and turn on a little battery powered lantern. But it only runs for an hour or two before it starts cooling off and I can plug the heat lamp back in. Tonight, my dd had a dance recital, so we had to leave at 5:30 to get her there at 6 and then the show was at 7 and didn't end until about 9:30. Then had to wait on her to finish changing, took MIL home, went and got some fast food and got home by around 10:40. So a little over 5 hours gone. At the time we left it was nearly 100 in the coop just from the heat of the day. We had one end open (like a window) a couple of inches (there is chicken wire over it) and because it was so warm, we left the light off. When we got home it had probably been dark for a good hour. It was plenty warm in there still-around 80 degrees-but dark. They were all piled together, probably because of the dark. So what would you do instead? Put in a 40W light and hope it doesn't heat it up any more? Or do the same thing we did tonight-I'm not wild about that because I hated to see that they were scared. Tomorrow night we have to do it all over again and it's supposed to be even hotter tomorrow than it was today. Today's high was 85 and breezy and tomorrow's is 90 (not sure about the wind tomorrow) and possible thunderstorms. I'm not sure if the battery lantern will run for that long (it uses 4 AA batteries).