I put my chicks outside in an unheated, uninsulated chicken house - but with a heat lamp in the brooder pen - at the age of 2 days. I only kept them in the house until the hatch was completely done. Then out they went. They are doing great. They're 3 weeks old now. I have a thick layer of pine shavings in the brooder pen. When the temps went below freezing for a couple nights the first week, I added a second brooder lamp - just to be safe. It was cold enough that the water was frozen in the waterers in the other pens. But the brooder lamp kept the chicken happy. There's only one lamp now, though - and they run all over the pen - just returning under the lamp when needed.