Empty, dry and refill a portable humidifier every day you use it, and give it a proper clean every third day. That's the EPA's guidance on home humidifiers. A proper clean means scrubbing off scale and film, disinfecting the parts that hold water, and rinsing several times so no cleaner ends up in the mist.
Why humidifiers get dirty so fast#
A humidifier is a tank of room-temperature water sitting in a warm room. That's ideal for bacteria and mold. The EPA notes that ultrasonic and impeller (cool mist) models tend to spray more microorganisms and minerals into the air than evaporative or steam models. Evaporative and steam units aren't immune, though. Any of them can grow things in water that's left standing.
The other problem is minerals. Tap water leaves a white crust on the tank and base, and in ultrasonic models the minerals can come out of the nozzle as fine white dust on your furniture.
The daily routine#
This takes two minutes and does most of the work:
- Unplug the humidifier. If it's a warm mist model, let it cool first.
- Pour out all the water left in the tank and base. Don't top it up. Adding fresh water to yesterday's just keeps old water in circulation.
- Wipe the tank and base dry with a clean cloth or paper towel.
- Refill with fresh water, ideally distilled.
How to clean a humidifier every third day#
Check your manual first. Manufacturers' instructions come first, and some models have parts that can't be soaked. Without specific directions, this is a sensible routine.
- Unplug it and take it apart. Remove the tank, cap, tray and any removable parts the manual lists. Keep the base with the motor and electronics out of the sink.
- Descale. Fill the tank partway with undiluted white vinegar and pour some into the base reservoir, then leave it to soak for 20 minutes or so, or as long as the manual says. Scrub the crust with a soft brush. An old toothbrush gets into the corners and around the ultrasonic disc, but be gentle with the disc itself.
- Rinse out the vinegar with plain water.
- Disinfect. If the manual doesn't name a product, the EPA suggests a 3 percent hydrogen peroxide solution, the ordinary kind from a pharmacy. Wipe or swish it over every surface that holds water.
- Rinse thoroughly. The EPA says to rinse with several changes of tap water so the cleaning chemicals don't get dispersed into the air. Three rinses is a reasonable minimum. You should smell nothing but water.
- Let everything air-dry, then reassemble and refill.
Never mix cleaning products in the tank. Vinegar and bleach together, for example, release chlorine gas. Do one, rinse completely, then do the next.
What about the wick or filter?#
Evaporative humidifiers have a wick, a thick paper or foam pad that soaks up water. Don't put vinegar, bleach or peroxide on it unless the manual says you can, because it can hold onto the chemicals and release them into the room. Rinse it in plain water if the manual allows.
Replace the wick when it goes stiff and crusty, discolored, or starts to smell, or on the schedule the manufacturer gives. A hardened wick also stops soaking up water, so the humidifier runs but doesn't humidify much.
Demineralization cartridges in ultrasonic models wear out too. If white dust starts showing up on furniture even though you have one, the EPA says that's a sign it's no longer removing minerals.
Quick schedule#
| Job |
How often |
| Empty, dry and refill |
Every day it's in use |
| Descale, disinfect and rinse |
Every third day |
| Replace wick, filter or cartridge |
Per the manual, or when it's stiff, crusty or smelly |
| Deep clean, dry and store |
End of season |
Use distilled water#
Distilled water is the easiest way to cut down on both scale and white dust, and the EPA recommends low-mineral water for that reason. It doesn't replace cleaning, since bacteria still grow in distilled water, but your descaling job gets much easier.
Be careful what you buy. The EPA notes that bottled water labeled "spring", "artesian" or "mineral" hasn't been demineralized, so it won't help. Look for "distilled" on the label. If you descale other appliances, our kettle descaling guide uses the same vinegar approach.
Signs your humidifier needs cleaning now#
- A slimy film in the tank or base, often pink, orange or greenish
- A musty or sour smell when it runs
- White crust on the tank, base or ultrasonic disc
- White dust on nearby furniture
- Mist output dropping off
If you see any of these, skip ahead to the full clean, even if it's not the third day.
Don't over-humidify#
A humidifier can make a room too damp. The EPA says not to humidify above 50 percent relative humidity, and its guide to mold and moisture puts the ideal range at 30 to 50 percent. A cheap hygrometer tells you where you are. If you see condensation on the inside of your windows, turn it down.
Storing it at the end of the season#
Do a full clean, then make sure every part is completely dry before you put it away. The EPA recommends storing it in a dry location. When you bring it out again, clean it before first use instead of filling a tank that's been sitting in a closet for months.
FAQ#
Can I clean a humidifier with bleach?#
Only if the manual says so, and then use exactly the dilution it gives and rinse very thoroughly. Bleach fumes in the mist are the last thing you want. The EPA's default suggestion is 3 percent hydrogen peroxide, which is easier to rinse away.
What about whole-house humidifiers?#
Furnace-mounted humidifiers have their own maintenance, usually a water panel or pad that gets replaced on a schedule the manufacturer sets. Follow the manufacturer's directions, and the EPA's advice not to let water stand in the unit for long periods applies here too.
Keeping up with it#
The daily empty becomes habit quickly. The every-third-day clean is the one people drop, so a repeating ChoreLists.com reminder helps during the dry months. If you also run a dehumidifier in summer, it needs a different routine, and an air purifier has its own filter schedule.