Attention: Airing in the summer increases the risk of mold in the basement

Attention: Airing in the summer increases the risk of mold in the basement

The hot summer visibly limits the comfort of the consumer. As soon as they enter their own four walls after a long day's work, they open the windows to exchange the musty air. This may be useful on the upper levels, but in the basement this behavior increases the risk of mold.

On warm days, ventilating in the basement has exactly the opposite effect: warm air that penetrates from the outside into the interior humidifies the cold air here. The result should actually be known to every human being, as he has already observed this scenario several times in his life: the mirror in the bathroom is fogged or a bottle from the fridge gets wet.

The warmer the air, the more water vapor it can absorb. On a muggy, warm summer's day, the water vapor saturation of outdoor air is up to 98 percent. Since a basement room has a temperature of 12 to 15 degrees Celsius (° C), airing here is disadvantageous in summer. The warm outside air enters the cool cellar. There, excess moisture condenses and settles on the walls. The consequence: Mold formation.

In the basement, airing is only on cool days.

Cellar rooms remain nice and cool even in summer, without having to ventilate. Ventilation is only recommended if the outside temperature is at least five degrees lower than the cellar temperature. This is not the case in many regions of Germany in the summer even at night. Temperatures rarely drop to the ten-degree limit.

In order to detect the ideal time to ventilate, consumers should attach a thermometer in the basement and one in the shade near a basement window. In this way they can always observe when the temperature falls below the required limit and ventilate accordingly. A low temperature alone is not enough to ventilate. In addition, the outside air should be drier than inside. To measure this value, there are so-called hygrometers (moisture meters). These are available for a few euros in the trade. For information on the different types and tips to buy, go here.

As an alternative to the hygrometer, consumers can determine the temperature by storing a bottle in the basement. If you put them outside and fog them, it's too hot to ventilate.

House and Basement Ventilation System

Modern homes are being made airtight. The problem: If not properly ventilated, the risk of mold increases. The correct ventilation is in turn tied to the daily routine of the residents. They leave the house early in the morning and return in the evening. Time to air remains so only in the early morning and late evening. By contrast, during the daytime, the air is trapped in one's own four walls.

In order to save on the ventilation process, consumers can use modern ventilation systems. They work with the help of sensors and regularly provide new, fresh air in the interiors. For Keller, there are special, decentralized fresh air systems: their sensors measure, among other things, the relative humidity inside and outside. Using these values, the system determines the absolute humidity and can provide adequate ventilation that dehumidifies the basement.

There are various subsidies for measures for domestic ventilation. The Federal Association for Home Ventilation (VfW) provides more detailed information.

Flooding: Special Ventilation Required

This article was previously only about the classic airing in the summer. At this time of the year, there may also be special cases that require special ventilation: assuming in early summer it has rained above average and the rainwater has flooded the basement. In this case, do-it-yourselfers first have to collect the water with a rag and a bucket and remove it from the cellar. Although it is relatively warm in summer, there is a high level of humidity after a rain shower. Together with the still wet floor in the basement there is a high humidity, which favors the formation of mold.

After the water is eliminated, do-it-yourselfers should set up a dehumidifier. This can reduce the room temperature in periods, if this is not possible due to the simple ventilation. A dehumidifier sucks in moist air and cools it down until it falls below the dew point. Then the moisture condenses in a special water tank of the device. Do-it-yourselfers must empty the container so that the dehumidifier can do its job.

Dehumidifiers are also suitable for use in the basement without flooding, especially in summer.

Room air in the basement favor

So that the room air in the basement does not work first wet, home improvement should pay attention to how they turn off their appliances, furniture and other things. Many basements are used as storeroom. The problem: The unneeded things are put on walls and rob this valuable space to breathe. Therefore: Do not place furniture or any other objects directly against a wall.

If the cellar is regularly ironed or clothes dried, the humidity increases. Through regular, correct ventilation, the humidity can be brought outside. If this is not possible (in summer, for example), the use of a dehumidifier is recommended.


In summer, the heat can reach the cool cellar when it is ventilated. Then the humidity increases and leads to an increased risk of mold growth. This problem can be solved with a proper airing and the use of a dehumidifier.

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