How often should you empty a humidifier?
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The short answer: every day
For a portable humidifier, EPA says to empty the tank, wipe all surfaces dry and refill it with fresh water every day. The point is to reduce the growth of microorganisms (germs such as bacteria and mold) in the tank. Unplug the unit first. A Honeywell manual for its ultrasonic cool mist models puts it simply: use fresh clean water every day.
Topping up is not the same as emptying
Pouring fresh water on top of what is left leaves the old water in the tank. EPA’s guidance is about not letting water sit: do not allow water to stand in the tank for extended periods, and keep the water clean. So pour it all out, wipe the tank dry, then refill.
When it is off or put away
A Honeywell warm mist manual says the unit should always be unplugged and emptied when it is not running. If it will sit unused for a week or more, the same manual says to follow its weekly cleaning steps first.
At the end of the season, EPA says to clean the humidifier as directed, make sure every part is dry, throw away used demineralization cartridges, cassettes or filters, and store it in a dry place. When you take it out again, clean it once more and dust off the outside.
Console and whole-house units
EPA’s daily rule is written for portables. For console humidifiers, EPA says to follow the manufacturer’s instructions for changing the water. For console and central (furnace-mounted) units, follow the maker’s cleaning directions, and if there is a tank, do not let water stand in it for long periods. More on the two types: whole-house vs portable.
Daily, every few days, at season’s end
| Task | How often | Who says so |
|---|---|---|
| Empty, wipe dry, refill (portable) | Every day | EPA; Honeywell cool mist manual |
| Scrub and descale | Every third day (EPA); weekly (Honeywell manuals) | EPA; Honeywell |
| Clean, dry and store | End of season, or before a week or more unused | EPA; Honeywell warm mist manual |
EPA’s every-third-day scrub is the strictest schedule. Your manual wins if it names its own. The scrub itself is in how to clean a humidifier.
Warm mist units: let it cool first
A steam (warm mist) unit holds hot water. Honeywell’s warm mist manual says to turn it off, unplug it and wait 20 to 30 minutes for it to cool before you refill. A Vicks warm mist manual says to turn it off and wait 15 minutes before refilling, and not to remove parts for 20 to 30 minutes after unplugging. How the two types differ: cool mist vs warm mist.
Water and humidity
EPA suggests water with low mineral content, such as distilled, to reduce scale and minerals released into the air: see distilled vs tap water. EPA also says not to humidify above 50 percent relative humidity: see winter indoor humidity.
Quick checklist
- Unplug, empty, wipe dry and refill every day (portable)
- Don’t top up old water; pour it out and refill
- Scrub every third day (EPA) or on your manual’s schedule
- Empty and unplug when it is not running
- Warm mist: let it cool before refilling
- Clean, dry and store at the end of the season
More: how to clean a humidifier · cool mist vs warm mist · all tips