Baby chicks need the temperature under the brooder lamp to be around 95 degrees F for the first week of their lives. To prepare them to move outdoors, lower the temperature by 5 degrees each week (so for week 2, lower it to 90 degrees), and so on, until you’ve reached current outside temperatures. That’s when they’re fine to put outside without a heat lamp. Now, if the weather is chilly, there is another rule of thumb to use. When they are fully feathered out and have lost all their “baby” down, which happens at around six weeks of age, they are ready to move outdoors. You can also hang the heat lamp in the main coop for the first few weeks that you move them out there, so they have some extra warmth for the transition. Baby chicks are a little like garden starts in that they do need to be “hardened off” before moving to outdoor conditions. Lowering the temperature by 5 degrees a week is what helps with the transition.