Our coop is just about ready for the pullets to move in (1st time chicken owners), but I'm still debating what to use on the coop floor. We live in western New York where summers can be hot and humid, and winters can be cold and snowy, with wind chills up to -15 during the worst days. Most of the winter's average temps are in the teens. I was going to use sand on the coop floor but read sand gets very cold in the winter. The coop has concrete floors, is 15'x15', and will have 6 chickens. What works best to keep a coop warmer- sand or pine shavings? I don't want to put something on the floor now only to change it in a few months. What do others in 4 season areas use on the coop floors? Thanks!!