Ventilating in fog may seem contradictory at first. You don’t want to let the moist air into your living space. But anyone who keeps the windows closed to keep out the fog is making a mistake.
Air that is too dry is unhealthy and can irritate the mucous membranes, while air that is too humid leads to mold formation in the living area.
Why ventilation is particularly useful in fog
Whether mold can form in the home depends on the relative humidity. This does not refer to the absolute amount of water in the air. Instead, relative humidity describes the percentage degree of saturation of the air with water – depending on the temperature.
Martin Brandis from the consumer advice center’s energy advice department explains it this way: “The warmer the air is, the more moisture it can absorb.”
Fog occurs when the outside temperature cools down quickly with high humidity. The cold air can then no longer hold the invisible water vapor. The vapor condenses, becomes liquid and forms mist. When ventilating, the opposite happens. The warm indoor air can absorb significantly more moisture than the cold outdoor air.
If you let foggy air into your home, the liquid evaporates and becomes invisible water vapor again. So the humidity drops again. So you don’t have to be afraid of mold, even in fog. You can measure the temperature and humidity with a hygrometer.
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