In addition to what's been said, in extreme climates like Germany and Minnesota, the window would completely frost over in January. Even modern low-e windows can't overcome -40°F, especially when indoor humidity is a bit elevated. Heat applied via radiator in that case or forced air in my case can help keep those lovely, desolate outdoor scenes visible.

In addition to what's been said, in extreme climates like Germany* and Minnesota, the window would completely frost over in January. Even modern low-e windows can't overcome -40°F, especially when indoor humidity is a bit elevated. Heat applied via radiator in that case or forced air in my case can help keep those lovely, desolate outdoor scenes visible.

_{* Apparently Germany isn't quite as cold as WWII documentaries led me to believe, but that doesn't change a thing about my answer. Frost can accumulate at any temperature substantially below freezing.}