What’s happening?
An ultrasonic humidifier doesn’t simply evaporate water; it atomizes it into tiny droplets, which then evaporate into water vapor.
If the water contains minerals (such as calcium or magnesium), those minerals do not evaporate in the process. Instead, they are released in the air as tiny particles. With mineral-rich water, these particles can sometimes be seen as white dust on nearby surfaces.
What does Ruuvi Air detect?
The mineral particles released by an ultrasonic humidifier are very small—typically within the PM2.5 size range, according to studies.
Because of this, Ruuvi Air correctly detects them as PM2.5 particles and reports higher PM2.5 values, even though the source is not smoke or outdoor pollution but the humidifier itself. Since PM2.5 measurement is also part of Ruuvi Air’s indoor air quality score (IAQS) , lower Air Quality readings are also reported.
Why does water quality matter?
The amount of minerals in the water directly affects the PM2.5 reading:
• More minerals in the water → more particles in the air → higher PM2.5 values
• Low-mineral or distilled water → fewer particles → lower PM2.5 values
How to reduce PM2.5 readings caused by a humidifier?
You can reduce fine particles and PM2.5 readings by:
• Using distilled, demineralized, or reverse-osmosis water
• Using a mineral-reducing filter in the humidifier, if supported
• Running an air purifier in the same room
• Placing Ruuvi Air away from the humidifier’s mist outlet
• Choosing an evaporative humidifier, which does not release mineral particles into the air
Summary
Ruuvi Air is working as intended when it detects increased PM2.5 levels near an ultrasonic humidifier. The readings are caused by mineral particles released from the water, not by smoke or outdoor air pollution. A lower indoor air quality score (IAQS) is also reported, since PM2.5 is part of the Ruuvi air quality score.
The long-term health effects of these mineral particles are studied, but not yet well understood.