Like everyone else American who's commented, I keep the windows closed if I've turned the heat on. I live in a very moist area of the country, but there's definitely nothing in the rental agreements about airing out an apartment during winter. I do find it gets stuffy, so any day it's warm enough that I don't *have* to have the heat on, I open the window for a bit, but ultimately I would rather be stuffy than cold, and really cold days are almost always dry anyway.

(I also grew up in a part of the country that only dropped below freezing at night, and that only for maaaaaybe a month. I don't handle cold well.)