September 10, 2025, 2:10 am | Read time: 2 minutes
To improve indoor air quality, air exchange is beneficial. Ventilation allows you to replace old, stale air with fresh air from outside. Breathing, cooking, and bathing vapors also saturate indoor air with moisture. High humidity in the home increases the risk of mold. Regular ventilation can prevent this. But what if the humidity outside is also high? Is it still advisable to ventilate, or will the humidity in the home increase further? myHOMEBOOK reveals how to ventilate properly in high humidity.
Ventilating in High Humidity–Yes or No?
There is no clear yes or no to this question. Whether you should ventilate in high humidity depends on the difference between the outside and inside air.
A brief excursion into thermodynamics: Air consists not only of nitrogen and oxygen but often also contains water vapor. As the temperature rises, the kinetic energy of the water molecules increases. The saturation vapor pressure increases. This allows the air to absorb more water vapor before it becomes saturated. This means that warm air can hold more moisture than cold air.
If the humid outside air is warmer than the air in the room, it cools down when it enters during ventilation. This increases the humidity in the room. Cool outside air, on the other hand, dries out indoors, and the humidity decreases. On hot, humid days, it’s better to keep the windows closed.
What to Consider When Ventilating in High Humidity
To avoid increasing indoor humidity, it can help to pay attention to the time of day when the outside humidity is high in summer. Mornings and evenings are usually cooler—the ideal time to ventilate.
An absolute no-go is ventilating with a tilted window. This can increase moisture in the walls, leading to mold both inside and outside on the facade. To exchange air quickly and effectively, you should open the window wide for five to ten minutes. Cross-ventilation is useful to shorten the ventilation time.
The most moisture is generated in the bathroom, bedroom, and kitchen, such as from long showers, cooking, or sweating and breathing during sleep. In these rooms, you should pay particular attention to short but strong ventilation intervals. A hygrometer can also help measure humidity. This way, you can see if the humidity inside decreases or increases after ventilation. Ideally, humidity should be between 40 and 60 percent.