I moved almost half of my 4 week-olds out to the transition coop. I'm so scared that something will happen to the heat lamp and they will freeze. It's still in the low-mid 30s at night here. My brooder was just getting too small. I tested out the transition coop and have a smaller shelter box immediately under the heat lamp. It was registering 87-102 in the shelter box. The rest of the coop is much cooler. This will sound harsh, but I moved the 6 that I thought most likely to be roosters out first to give it a try. These 6 are the largest with the most prominent combs and are the most aggressive. I want gentle layers, so these guys will be given away at some point if they survive this transition.