How to ventilate properly – now more important than ever

With today’s construction methods, homes are better insulated than in the past. This saves energy, but also reduces the natural exchange of air. Buildings with new, tightly closing windows in particular often lack “automatic” ventilation via small leaks. The result: moisture builds up, mold forms, wallpaper comes loose and unpleasant odors develop. In most cases, the cause is not the building, but incorrect ventilation behavior.

Why ventilation is so important

Indoor air always contains water vapor – invisible, but measurable. The colder the air, the less moisture it can absorb. When it cools down, the water vapor settles as condensation on cold surfaces such as windows or exterior walls.

When cooking, showering or drying laundry, the humidity also increases. Plants, aquariums and people also play their part. Without regular air exchange, the moisture cannot escape – and mold is often the result.

How to ventilate properly

• Ventilate briefly several times a day: Open windows fully three to five times a day – for five to ten minutes in the morning, at midday and in the evening.
• Cross-ventilation is ideal: if possible, open windows on opposite sides and ensure a draught.
• No permanent ventilation: Tilted windows in winter cause energy losses and cool down walls and furniture.
• Heat rooms evenly: Even rooms that are rarely used should not cool down. If a room is deliberately kept cooler, keep the door closed. This prevents warm, humid air from flowing from the heated areas into the cold room. As cold surfaces absorb moisture from the warm air, this temperature difference can lead to condensation on the walls of the unheated room and thus to mold.
• Allow air circulation: Do not place large furniture directly against external walls – a distance of around ten centimeters is sufficient.

You can also ventilate when it rains: Warm indoor air absorbs moisture and transports it outside.

Guide values for an optimal indoor climate

During the heating period, doors between rooms with different temperatures should remain closed. When ventilating, on the other hand, open all doors to speed up the exchange of air.

Special feature: Ventilate the cellar properly

Basement rooms need special attention. When warm, moist air meets cool cellar walls in spring or summer, condensation can form. Therefore:

• In summer and spring, only ventilate at night or in cool weather.
• Ventilate regularly and briefly in winter – similar to living rooms.
• Avoid permanently open cellar windows.