February 11, 2025, 9:08 pm | Read time: 4 minutes
When it’s freezing cold outside, you want to keep the window closed. However, this is not a solution either because otherwise, there is a risk of mold. Can so-called “micro-ventilation” help here?
There are two primary methods to ensure fresh air in your home: fully opening one window or opening multiple windows to create a cross breeze. Alternatively, you can tilt the window to allow for ventilation without letting in too much cold air. However, the first method is particularly recommended, as leaving the window tilted for an extended period could excessively cool down the home. But there is also a third option, at least with modern windows. With these, you can adjust the settings for micro-ventilation, also referred to as “gap opening” or “micro ventilation.” What’s this all about? myHOMEBOOK asked an architect and consultant for energy-efficient renovation.
How Micro-Ventilation Works with Windows
Modern window systems offer more than two options for ventilation. In addition to complete opening and tilting, these windows can also be “micro-ventilated.” This is achieved by positioning the window handle at a 45-degree angle, which is neither fully vertical nor horizontal. This creates a small gap between the window and the frame, through which fresh outside air can constantly flow in and humid inside air can flow out.
How Can I Tell If My Window Has This Function?
Property owners usually know which windows are in their homes. This is not always the case for tenants. The easiest way to find out whether the windows have gap ventilation is to try them out. However, you should proceed with caution. First, turn the handle to 45 degrees – i.e., between the “open” and “tilt” positions. Then, carefully pull the window towards you. If it opens a few millimeters, the micro-ventilation is working.
Is the Savings Adjustment Worth It?
Rita Maria Jünnemann is an architect and consultant for energy-efficient construction and renovation at the NRW consumer advice center. She sees micro-ventilation as a “supplementary option” that can definitely be worthwhile. However, as always, it depends on the circumstances.
“When ventilating, the humidity should get out as quickly as possible, which is not possible with this type of ventilation,” explains the expert when asked by myHOMEBOOK. “It’s better to open the door wide once; that’s the quickest way.” Continuous ventilation, even through a small gap, poses a risk of the apartment becoming too cool.
However, Jünnemann does see one way in which opening the gap could be worthwhile – “at night in bedrooms when there is a risk of the CO2 content becoming too high”. Micro-ventilation ensures that CO2 is removed evenly so that you don’t wake up in the morning with a “heavy head.” The energy expert would also recommend micro-ventilation if the home has been damp for a long time. “At the moment, you can dry an apartment well, as the outside air contains hardly any water,” explains Jünnemann. This would allow the moisture to escape without losing much heat.
“When it comes to ventilation options, we are also dependent on the thermal conditions,” says the architect. If there is no wind, or if you live on a lower floor in the city, you have less air exchange when ventilating economically.
What About Burglary Protection?
Even if the window is apparently closed with micro-ventilation, burglars have an easy time of it, warns Jünnemann. In terms of burglary protection, this technology is just as insecure as a tilted window. Therefore, this presents an easy opportunity for burglars, which is why you should not leave your home unattended with the window in a tilted position.
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Expert tip: Combine with Sensors
To increase the effectiveness of micro-ventilation, the system can also be combined with sensors that measure CO₂ and humidity in the room air. This type of ventilation would then be particularly suitable – and the sensor would sound the alarm when it’s time for fresh air. “We’re already moving in the direction of a ventilation system, which already ensures even air exchange in many new buildings,” says Jünnemann. Naturally, the more effectively a building is insulated, the less heat will be lost.