My 5 chicks are about 6 weeks old now and they have been in the garage in a playpen unheated for the last 3 weeks. No problems, they seem to keep each other warm. We are almost done with the coop and will be putting them outside here soon. the temps for this week will be around 40-mid 40's at night. I imagine I don't need a heat source for them out there? but have seen people recommending a light? I just want to make sure before i put them out for the night.