At our coldest we had -29 with -36 wind-chill and all of my birds did just fine with only doing one thing differently. The only thing I did different was to close my north facing vent. So what I learned is that they are WAY hardier than we give them credit for!
My laying coop is un-insulated except for the roof and has 3 Plexiglas windows, my silkie coop is insulated from top to bottom, and I have 7 naughty roos living in my barn instead of their coop (they snuggled into the hay though so were just fine).
When we know it is going to drop below zero, we've been closing the ventilation window. The coop is fairly large and quite dry. The chickens are always locked in the coop at night, with the pop doors accessing the run, closed down.
Imagine my surprise when I went out to check on them one -10 degree morning, and saw a lone chicken out on the roost in the run! DH had not checked the run when he shut them in. The Welsummer managed the -10 night just fine, without anyone else to provide body heat.
Originally, I thought I might need to provide some heat when it hits -25, but after that experience I think they will be fine if they can huddle together with the window closed. It looks like we'll find out how they do this weekend.
Make that South Texas, it was 18 this morning in Texoma (I know spring temps for you all up north) Still bring in the waterers at night rather than wrestle with ice blocks in the morning. Only a couple more weeks I hope.