Oldhen has given you excellent advice, especially about ventilation. One of my south-facing windows is always at least a little bit open to allow fresh air to enter and moist air to vent.
We are expecting temperatures down into the zero range here as well, possibly colder. As well as another anywhere from three to six inches of snow on top of the foot we already have over the next few days. I don't count wind chill, as it only counts if you are actually stupid enough to stand in the wind for very long