What I did with my chicks is at 4 weeks old I put them out and here in Washington its quite cold but they seemed fine. But just in case for the first couple of nights we put a heat lamp up in the coop. They are now 7 weeks old and we are using the heat lamp for 2 more chicks. Be sure to fill their water bowl up 3 times a day on hot days with cold water. The chicks will drink when they get too hot and cold water will refresh them and cool them down!! Also make sure they ALWAYS have access to shade!!