Minimum Humidity 40 Percent: Establishing Healthy Humidity Levels
Dry air is a particular problem during the winter heating season: on one hand, too-low room humidity worsens the important sense of comfort. On the other hand, it leads to an increased risk of infection – for example from flu viruses. That's why a trade association launched the Minimum Humidity 40 Percent campaign.
Humidity generally describes the water vapor content in the air. It's measured as absolute humidity in grams per cubic meter and is defined as the mass of water vapor contained in a defined volume of air.
Maximum humidity plays a decisive role as a second variable: it's defined as the highest possible absolute humidity at a given temperature. Relative humidity, finally, is the percentage ratio between the absolute and the maximum humidity.
What relative humidity is recommended?
A relative humidity between 40 and 60 percent is recommended. However, this often isn't achieved, especially in public buildings. This is one reason why the Fachverband Gebäude-Klima e.V. (FGK) launched the Minimum Humidity 40 Percent campaign. "The campaign's goal is to raise more awareness of the issue among building owners, planners, commercial users, and employee representatives," explained Claus Händel, Technical Officer of the FGK, when the campaign was presented at the Elbphilharmonie in Hamburg.
Air that's too dry worsens the skin and affects the eyes and mucous membranes. Our health, our performance, deteriorates. "Especially in public buildings with high visitor numbers, the minimum humidity of 40 percent is fundamentally important," emphasized Dr. med. Walter Hugentobler, specialist physician and expert on indoor humidity.
"Minimum humidity of 40 percent helps significantly reduce the risk of infection and increase health and well-being."
When is humidity too high?
For living spaces, the ideal values for relative humidity are between 40 and 60 percent – usually at a temperature between 20 and 23 degrees (children's rooms, living and working spaces) or between 17 and 20 degrees Celsius in the bedroom. In the bathroom, relative humidity may be somewhat higher (50 to 70 percent) – but it's recommended to reduce humidity by ventilating after showering and to close the bathroom door so that steam doesn't accumulate in poorly ventilated areas.
If relative humidity is too high, with more than 60 percent on a sustained basis, the threshold for mold growth is exceeded – provided the exterior walls are significantly colder than the indoor air temperature. Most mold species prefer a relative humidity of 80 percent at a temperature of 20 degrees Celsius, but some species can also develop at lower humidity.
The spores and VOC gases from mold can, when inhaled, cause various other complaints besides allergies. These include, among others, migraines, asthma, coughing and colds, conjunctivitis, as well as skin changes, joint pain, and gastrointestinal complaints.
What influences humidity in buildings?
Room humidity largely depends on the usage habits of the occupants (frequency of showering / cooking), but also on ventilation behavior. In winter, unregulated ventilation can worsen the problem of low humidity. Environmental influences, such as work materials (e.g. paper), furniture, or carpets, also play a role. Plants, aquariums, or indoor fountains also affect humidity.
In offices, department stores, or other public buildings, the problem of overly dry room air is made worse by the fact that there's no additional moisture from showering or cooking. Many people with many potential sources of air pollutants make higher air exchange necessary.
However: in winter, classic ventilation lowers room humidity: because the cold outside air enters a warm room, it warms up from, say, 0 to 22 degrees Celsius. The relative humidity of this warmed air can therefore be no more than 20 percent.
Measuring humidity, is humidification necessary?
"Humidification should generally be planned for in all areas where relatively large amounts of fresh air are needed. For example, in offices, shopping centers, or restaurants," recommend the FGK representatives on the website for the Minimum Humidity 40 Percent campaign.
In the home, you can use the air-Q air analyzer or another hygrometer to permanently monitor room humidity and establish healthy humidity levels. If it's below 40 percent, humidification is strongly recommended here too.