Well, I live in NH as well, and it certainly has been cold! We've had a hard frost for the last week (with the exception of one night where we got a little rain).
Our coop has sofits under the edges of the roof and a pretty typical ventilation grate just below the top of the peak on the front.
My understanding was that it was advisable to avoid condensation, because it's not so much the cold that bothers well feathered, healthy birds, but hyperthermia caused by dampness (it's the same for my bees btw). Allowing for some movement of air helps to keep things dry, and the addition of a heated waterer (and maybe a red light, I'll have to see how cold it really gets) is really all I plan on doing. My coop is in a sheltered spot, but the 1/2 glass door faces South.
-Christian