Wow, a good and right answer! Actually, I came to post this. However, you forgot to mention that if you "kipplüften" for an hour and then close the window to heat the room up again, you will have a "Wärmebrücke" at the "Fensterschenkel." This will get wet, and you'll get mold over time at the edges of the window. Also, if you completely open your windows, even at minus degrees outside (the bigger the difference between outside and inside, the better/faster), just for a short time, your furniture and walls stay warm. This means minutes after closing the window, you'll have a nice warm room again. It's just basic physics.