The large fireplaces I just looked at, the Quad 7100 and FPX 36 and 44, require air cooled chimneys, I believe their own systems. How does that work in a cold climate? With that and the outside air, I can see a lot of coolness coming in when the unit isn't working. On the plus side, my Heatilator has the same system as the Quad, and Northstar.