Window constructions commonly used in the USA facilitate relatively easy installation of fans.

Special window fans can be easily inserted into open windows. In our experience, such a fan on a low to medium setting, combined with a slightly open window on the opposite side of the room or in another room, is sufficient to maintain the CO2 concentration in a room with two people below 600 ppm. Especially when sleeping or engaging in sedentary activities, the CO2 level should, in our experience, be kept below 650 - 700 ppm.

The fans should only generate a light breeze to ensure optimal air circulation. Additionally, the slight overpressure created in the building can help prevent pollutants, which would normally enter through cracks in the masonry, from reaching or remaining in the room.

However, if the air is blown out of the room, air can enter the room uncontrolled from various places, leading to less effective air exchange and potentially to an accumulation of pollutants.

Air Filters

To further improve air quality, we strongly recommend the use of a fine dust filter.

Unfortunately, we have not yet found a window fan that is already equipped with such a filter. Therefore, we have decided to attach a commercially available fine dust filter to the fan using adhesive tape. This DIY solution allows us not only to circulate the air but also to clean it of fine dust particles.

Since particularly small particle sizes can cause significant harm, we recommend using fine dust filters capable of filtering particles as small as 1 micrometer (PM 1). These types of filters offer more effective protection against microscopic pollutants that can cause health issues.

The effective use of a window fan with a fine dust filter can make the use of additional indoor air purifiers unnecessary. The often-advertised activated carbon filter in air purifiers, typically used in the form of mats, is largely ineffective for cleaning indoor air. Its filtering performance does not significantly improve the quality of indoor air. This is often evident from the fact that these products do not specify an absorption rate for gases, unlike what is typically stated for fine dust filtration.

 Why air purifiers can make u sick

Pro an Con


  • Cost-effective in terms of acquisition.
  • Efficient in air exchange.
  • Effectively purifies the room from fine dust, viruses, and bacteria when used with filters.


  • Not energy efficient when heating or cooling is involved.
  • Potential disturbance due to noise generation.