Where do you live to get a low of -25 this time of year? We only hit -8 F this morning. Oh wait, I get it. Your in Canada and use that easy system of 0 is freezing and 100 boils water. So my low this morning is on par with yours if indeed your Celcius (-8F = -22C). My coop is unheated and uninsulated.
I'd like to see a picture or have a better description of your ventilation system. To me as described so far it doesn't sound like enough. If the moisture of coop is not dispelled (vented out) enough large combed chickens will experience frostbite at freezing point of water. Too many warm bodies in a poorly vented room will produce a lot of moisture. The humidity level and temperature to make frost are hand and hand. Lower the humidity in the coop and it can withstand lower temperatures before producing frost.
I suppose I can say a bit more on ventilation. There are two methods of ventilation. First being a huge opening for passive air exchange. Cold weather that is not an option unless your coop is large enough to have the roosts far enough back from the hardware clothed south facing wall that wind isn't an issue. Look up Woods Style Coop designs. Really nice for large coops and cold climates. The other type of ventilation is to have an inlet and outlet. Via convection air is pulled in the lower inlet and forced out the higher outlet. The physical action is forced air without fans. You get quite an increase in air flow by laws of physics not fans or large openings. If there is enough of a pitch to your roof then inlets are on the lower eve and outlet higher eve, or if a gabled roof inlets both eves and outlets both gable ends. Ventilation made easy is a single slant roof with plywood sheathing lower by 2-3 inches under top and bottom of slant roof. Cover openings with hardware cloth. So the roof joist would be the opening depth, either 2x4 laid flat (1.5 inches) or 2x4 upright (3.5 inches). The longer roof board makes for the spacer on top of the end wall.
Edited by Egghead_Jr - 12/16/16 at 5:14am