Our chickens spent their first freezing winter in their 4'x4' insulated,unheated coop. There were minus degree temperature overnight, and near zero during the day Except for a few nights during the blizzards, our coop windows are always wide opened 24/7, and there are also several permanent vent holes, providing one sq. ft. of ventilation per chicken.
Our coop is also equipped with a temperature and humidity guage so we know exactly how cold and how humid it is.With the vent holes and windows open, the temperature inside and outside are equalized during the winter. The insulation really did not have much effect in warming up the coop if there is no internal heat source. We monitor the humidity level a lot more closely than the temperature since chickens can keep warm themselves, but need help in having good ventilation. In the summer however, the interior of the coop is much cooler due to the insulation and ventilation. I spent more time and effort in the winter to shelter their run from rain, wind and snow, so that our chickens always have the outdoor activity space no matter the weather conditions. They never stay inside the coop except for sleeping and laying.