This is my first winter with chickens and living in central Minnesota I have concerns that they will stay warm enough in our cold winters, especially when we hit -20 (actual temps not wind chill). I've read a lot of great information here with recommendations both for and against adding heat to a coop but still am unsure of what to do. My biggest concern with using any form of supplemental heat is the risk of fire. I live on a 20 acre heavily wooded property, which is surrounded by hundreds of acres of woods, so a fire would be beyond devastating. I have 4 chickens (2 orpington, 1 maran and 1 brown leghorn) in a 4'w x 7'd x 6'h coop with an attached run. I've covered some of the run walls with plastic to help block the wind during the winter. I close the pop door at night but open it every morning as their food and water is in the run. I built the coop out of pallets (I didn't have time to add wood siding to the coop this year but will do that in the spring) and have lined the inside walls with straw for a bit of winter insulation. I have venting at the top of the coop walls that is always open and three windows, which are currently closed but that can be propped open if needed. I'm using the deep litter method and it is very dry in the coop - no indication of moisture anywhere. I am going to add some additional straw to the inside of the coop for the girls to nestle in but am wondering if that will be enough to keep them warm enough. We've had low temps of 7 degrees overnight and all are doing fine. In addition to their regular food I give them some black oil sunflower seeds in the afternoon and will add a little cracked corn as well. My main concern is when temperatures drop into the negative range. Any thoughts or suggestions would be very much appreciated!