If you have mold in the apartment, it can be due to the wrong ventilation. Those who want to save on heating costs, in particular, open the windows too seldom - and risk damage from moisture.
Heating costs have exploded. Who can afford to regularly ventilate the heat outside? But this is important for your own health and for the building. However, there is a small device that can help you not to overdo it with venting the heat on bitterly cold days: the hygrometer. The cheapest devices are available for less than 10 euros, but you can also spend more than 50 euros on them.
But let's look at the problem first: Why do you actually have to ventilate warm air on winter days? The answer: it can carry much more water vapor than cool air. The air humidity in the room is reduced by airing out the warm indoor air and airing in the cool outdoor air. And if this is low, the risk of the formation of mold that is hazardous to health decreases.
And the short-term ventilation surprisingly has a financial advantage: "The more humid the air in the room, the more energy you need to heat it up," says Wolfgang Lorenz, deputy chairman of the Federal Association for Mold Remediation.
The hygrometer measures the humidity in a room. If it is only above 65 percent for a short time, that is not a problem. However, values of over 70 percent over a longer period of time are problematic. "Values between 50 and 60 percent are desirable," says Jörg Friemel from the North Rhine-Westphalia Chamber of Engineers. His advice: if the humidity is higher, you should ventilate. "And until the values are back in the unproblematic range."
How quickly the freshly ventilated air is enriched with moisture again varies. But one thing is clear: Neither the values immediately after ventilation nor the optimal values between 50 and 60 percent humidity are permanent in the room - our actions contribute to this. Showering, cooking, drying laundry - all such activities that are associated with moisture naturally drive up the humidity strongly and quickly. And not only that: our normal breathing and sweating also drives the values up.
If you want to save energy, you are well advised to place several hygrometers in the apartment and keep a close eye on them. Wolfgang Lorenz advises at least two devices - "one in the coldest room and one in the wettest room in the apartment".
The coldest room is often the bedroom, and the wettest areas are the bathroom and kitchen. The devices should not be in the middle of the room, but in the coldest spot. This is an outside wall, or better yet, the corner between two outside walls. These are the areas where moisture settles first.
Hygrometers help to gradually find out how the air humidity changes in the course of the day in the respective house or apartment. And how long it takes to ventilate the desired values. Because: "If you air the room too briefly, moisture will still remain in the room," says Jörg Friemel. "But if the windows are left open for too long, you ventilate a lot of the expensively generated energy." In the process, parts of the building also cool down, which then have to be heated up again - so you pay extra here too.
"How long you have to ventilate depends on how high the room temperature is and what the outside temperatures are. And on the humidity inside and outside," says Friemel. As a rule, however, the necessary ventilation time is between 10 and 15 minutes.