Humidity: 40–60, and no guessing about the humidifier
In winter the heating dries a room to a desert-like 15–20 %; in summer damp above 60 % feeds mould. Between them is a narrow band where everyone is fine.
Which numbers are normal
The zones on the device screen. Colour appears only where attention is needed.
| 40–60 % | comfortable |
|---|---|
| 30–40 and 60–65 | attention |
| below 30 or above 65 | out of range |
GOST 30494-2011; SanPiN 1.2.3685-21; WHO 2009 (mould); EPA
How it looks on the device
Real frames from the device, captured on 4 September 2026.
Why it matters
At 40–60 % there are the fewest airborne viruses, mould on walls and dust mites in bedding at the same time.
In dry air the nasal lining traps viruses worse, and cough droplets dry into tiny particles that hang in the air for over three hours instead of eight minutes.
Dust mites do not drink; they absorb moisture from the air. Below 50 % they die within 4–11 days. That works more reliably than any spray.
Mould germinates at 75–80 % on a surface, but in corners and on cold windows humidity is higher than the room average, which is why WHO draws the line at 60 %.
Arundel et al. 1986; Kudo et al. PNAS 2019; WHO Dampness and mould 2009
What the device says
Hints in words on the screen. Actions about the room, not about the body.
- “No humidifier today” — if humidity is mid-range.
- “The air is dry” — below 30 %: switch on the humidifier or hang a wet towel on the radiator.
- “Damp” — above 65 %: air the room or run the extractor, check corners and windows.
Questions
- Why is humidity 60 in summer and it does not feel dry?Humidity is relative: at 25 °C the air holds twice as much water as at 15 °C for the same percentage. The feeling of dryness depends on temperature.
Other readings: Carbon dioxide · Temperature · Pressure · Light · Noise · Weather outside