I use a chicken A-Frame tractor, Once they are 2 weeks old.. Having a MUCH colder side of the "brooder" while stil having a warm light to warm up under, Causes my chicks to be much healthier then when I keep them inside for 5 weeks.... My last two batches (16, and 17) Were kept outside once they hit 14 days old... and they are MUCH healthier than my other birds.