i would open the door and let them have a wander outside if they want.
this have a twofold benefit of venting the coop in addition to keeping them happier.
the snow is still coming down here (the good meterologists predict over forty cm) but i managed to shovel out a path and everyone had a wander for the past three hours. it keeps them from getting snarky with one another plus the goats all urinated at least one outside. (my chooks share with ducks, pony, goats, et cetera.)
humidity will always happen even if you just have chickens in there; this is owing to having fresh water, which evaporates into the dry winter air and the chooks' exhalations..., as you know when we expire we release warm air (the warmth is due to the water mostly).
as the mammals were unimpressed with the snow, I have left the pop door open to permit the birds out. i can only see one duck outside right now but my snow blower might have unsettled them with its coughing black smoke.
let me know how you fare; frostbite is the most difficult thing that i have had to deal with recently with my last rescue. wallace, our newest bantam rooster, was found in downtown montreal. when i picked him up from the shelter he had black spots from frostbite on his comb. he is going better now but my guess is that he had been dumped while it was snowing and snowmelt damaged his comb.