Winter: Closed. It can get to -25C where I live, and I need to sleep with the window open. I don't want the rest of my house ruined with the door open.
Summer: depends on the heat. If OK, closed. If too hot, door ajar
edit: plus im guessing they live in norway or finland (ignoring sweden cuz fuck sweden) or canada. And we are used to the cold. Ive gone to school (2.7km at the time) in -33 C without gloves and normal clothes so