I have a barn coverted into a coop with an outside run. I have been opening the bard door for them in the morning and leaving them out until I get home from work at night (dusk). Since its a full regular door, and it blows cold air in, I am wondering at what point do I keep them closed up and inside? They have plenty of space and many choose to not even go outside. (12 x 24 ft inside for 15 chickens) At what tempurature do you keep them inside?