Choosing a humidifier
How to choose a humidifier for a room
Both WetAir models are ultrasonic and produce about 300 ml of mist an hour. They differ in tank size, recommended room size, placement and care.
Updated:
The short answer
For a room up to 35 m², MH-204 with its 2.3-litre tank will do — about 7–8 hours at full output. For a larger room, or fewer refills, look at WH-411: a 4-litre tank, a recommended 20–40 m² and about 13 hours. Both need clean water no warmer than 40 °C and regular cleaning, and you should monitor room humidity with a separate hygrometer.
MH-204 or WH-411: a comparison from the manuals
The same mist output, but different tanks, room sizes and placement rules.
| MH-204W / MH-204B | WH-411B / WH-411W | |
|---|---|---|
| Mist output | 300 ml/h | 300 ml/h ±10% |
| Tank | 2.3 l — about 7–8 h at full output | 4 l — about 13 h at full output |
| Recommended room | up to 35 m² | 20–40 m² |
| Controls | mechanical, rotating nozzle | ring: ON, more, OFF; fan dries the channel for 3 min after switch-off |
| Where it stands | level surface at least 60 cm above the floor, 10 cm from the wall | firm, level surface, mist away from wallpaper and electronics |
| Routine care | water daily; chamber, float, transducer once or twice a week; cartridge ~400 l, if fitted | water daily; clean weekly, every two days in continuous use; sponge monthly |
Both models draw 25 W. Neither manual describes automatic humidity control, so use a separate hygrometer. The comparison does not rate how fast a particular room will be humidified.
How an ultrasonic humidifier works
A disc vibrates at high frequency and turns water into a fine, cool mist that a fan carries into the room. Both models draw 25 W and run quietly. The mist is not hot, but never aim it at wooden furniture, books, wallpaper or electronics: moisture will settle on them.
Room size and real-world results
According to the manuals, MH-204 suits a room up to 35 m² and WH-411 a room of 20–40 m². These are guides: a high ceiling, open doors, airing and dry heated air all slow the rise in humidity. Use a hygrometer so you neither over-dry nor over-humidify; the WH-411 manual names 40–60% as the most comfortable level. If condensation appears on windows or walls, reduce the output or switch off.
Tank size and running time
Running time is roughly the tank volume divided by the output. MH-204: 2.3 l ÷ 0.3 l/h — about 7–8 hours at full output; WH-411: 4 l ÷ 0.3 l/h — about 13 hours. At lower settings it runs longer. Both models stop producing mist when the water runs out; on WH-411 a red light comes on.
Controls and placement
MH-204 has mechanical controls and a rotating nozzle. Its manual requires a level, stable surface at least 60 cm above the floor and at least 10 cm from the wall — not the floor. WH-411 uses a ring: turning it clockwise increases output, OFF switches it off, and the fan runs for another 3 minutes to dry the channel. Stand WH-411 on a firm, level surface so the mist does not reach wallpaper or electronics. Neither manual describes automatic control of a set humidity.
Water and care
Both manuals require clean cold water no warmer than 40 °C — drinking water that meets the standard, or distilled — changed daily. Hard water leaves white dust on furniture and scale inside; MH-204 may have an optional water-treatment cartridge rated for about 400 litres. Check what is supplied with your unit. For WH-411 the manual advises cleaning once a week, or every two days in continuous use; scale is removed with a glass (200–250 ml) of 5% white vinegar over 15–20 minutes, and the dust sponge is washed monthly. Never add oils or fragrances to the tank.
Humidifier checklist
- Compare the room with the guide figure: MH-204 up to 35 m², WH-411 20–40 m².
- Work out running time: tank volume ÷ 0.3 l/h.
- For MH-204, plan a surface at least 60 cm above the floor and 10 cm from the wall.
- Buy a hygrometer: the output control does not show room humidity.
- Decide which water you will use and set aside time for cleaning.
Common mistakes
- Standing MH-204 on the floor or against the wall.
- Aiming the mist at furniture, books or electronics.
- Topping up yesterday’s water instead of changing it daily.
- Adding essential oils or detergents to the tank.
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WetAir manuals and support
Check the exact model requirements
If the humidifier is noisy, produces no mist or the membrane has scaled up, clean it as the manual describes first; if that does not help, contact WetAir service.
Models to compare
Sources and verification
Specifications, water requirements, placement and care come from the WetAir MH-204W/MH-204B and WH-411B/WH-411W manuals (the WH-411 room size is from its specification table). Running time is simple arithmetic from the rated output; it is longer at lower settings. EPA advice on fresh water is context only.
Frequently asked questions
What room size does a 300 ml/h humidifier cover?
According to the manuals: MH-204 up to 35 m², WH-411 20–40 m². In a large room with a high ceiling or frequent airing, humidity will rise more slowly.
Can I use tap water?
The manuals allow drinking water that meets the standard, or distilled water, no warmer than 40 °C. Hard water leaves white dust; use purified or distilled water, or check the compatible optional MH-204 cartridge if fitted.
Why did the humidifier switch itself off?
Most likely the water ran out: both models stop producing mist when the tank is empty. On WH-411 a red light also comes on.
Does it hold a set humidity?
No, the manuals describe no such function. Watch a hygrometer and reduce output if humidity goes above 60% or condensation appears on the windows.