This is the first winter with our chickens. We have had some cold temps near 0 and the 4 girls have been fine. Now on sunday we are supposed to have a low temp of -14, located in northern indiana near chicago. Im going to keep the coop closed up that day. I have between 6 and 8 inches of pine and straw bedding in the coop. My coop is 4ft by 4ft, i keep a light in it but its not a heat lamp. Do i need to add any heat to the coop or will the 4 chickens be fine in the 4x4 space?