https://www.theguardian.com/world/2020/sep/30/germans-embrac...
> The custom is something of a national obsession, with many Germans habitually opening windows twice a day, even in winter.
> Impact ventilation, or Stosslüften, which needs explanation for most people unfamiliar with Germany except for experts in air hygiene, involves widely opening a window in the morning and evening for at least five minutes to allow the air to circulate. Even more efficient is Querlüften, or cross ventilation, whereby all the windows in a house or apartment are opened letting stale air flow out and fresh air come in.
> In Germany, windows are designed with sophisticated hinge technology that allows them to be opened in various directions to enable varying degrees of Lüften.