This “Stoßlüften” is just opening a couple of windows for several minutes to create a draft. There’s a nice booklet about ventilation for regular Joes called “

This “Stoßlüften” is just opening a couple of windows for several minutes to create a draft. There’s a nice booklet about ventilation for regular Joes called “Richtiges Lüften in Wohnungen” (Proper ventilation in apartments) published by the Fraunhofer IRB (i.e. information centre for inner spaces and construction). This booklet explains the role of material and air humidity, how ventilation became important as buildings became more airtight, how relative humidity works, etc. A key observation is that the main purpose of such intense ventilation is refreshing the air, i.e. removing unpleasant smells and CO2. Landlords, experts and courts of law have nevertheless settled on the idea that 2-3x intensive ventilations per day are necessary to avoid mould. The booklet claims that dehumidification is ideally achieved through “Spaltlüften”, which is keeping a window partly open for a longer period of time: the cool outside air enters the room in small quantities which can be quickly heated, thereby drying said air and enabling it to absorb additional humidity. Due to the longer ventilation period, materials which absorb humidity such as drapes, carpets, wallpaper or plaster can release said humidity which shall be absorbed by the dry air and ultimately exchanged with outside air. The heater must stay permanently on so that the cool air can be heated. Some apartments have passive mechanical ventilation such as openings in the rubber seals of the windows or ventilation slots in the window frames which follow this principle.