Humidifiers

A humidifier adds water vapor to dry indoor air, which matters most in winter, when heated outdoor air ends up far drier than it was outside. Used well, it keeps a room in the comfortable middle range. Used carelessly, it can over-humidify a room, spread minerals as white dust or grow bacteria in its tank. The guides in this section cover both sides, based on EPA, CPSC and MedlinePlus guidance and on manufacturers’ own manuals.

First, check whether you need one

Buy a hygrometer before you buy a humidifier; our guide on how to check humidity in the house explains which kind to get and where to put it. The EPA recommends 30% to 50% indoors and says not to humidify above 50%; in a cold snap, NDSU Extension suggests 30% to 40%, because above about 40% windows and other cool surfaces start to collect condensation. Our guide to the ideal indoor humidity explains how to adjust through the seasons. Two calculators help here: the relative humidity calculator shows why heated winter air gets so dry, and the dew point calculator shows at what humidity your windows will start to fog.

Pick the right type

• Evaporative (wick) humidifiers blow air through a wet wick. The EPA says they, like steam units, generally aren’t expected to spread substantial amounts of minerals, and their output slows as the room gets more humid (Honeywell’s HCM-350 manual says its unit puts out little moisture above 60%). See the best evaporative humidifier.
• Ultrasonic and impeller (cool mist) humidifiers make a visible mist without heat, but the EPA says they generally disperse the most minerals and microorganisms, and they’re the source of white dust, so water and cleaning matter more.
• Steam and warm mist humidifiers boil the water. MedlinePlus advises cool mist for children because warm mist can burn, and the EPA says to keep steam vaporizers out of children’s reach. Compare both in warm mist vs cool mist humidifiers.

Humidifier types at a glance

Type	How it works	Minerals in the air (EPA)	Burn risk
Evaporative	Fan blows air through a wet wick	Not expected to disperse substantial amounts	No
Ultrasonic	Vibration makes a cool mist	Among the most; can leave white dust	No
Impeller	Spinning disk throws a cool mist	Among the most; can leave white dust	No
Steam / warm mist	Heats the water	Not expected to disperse substantial amounts	Yes: keep away from children

New to all this? Thinking of an essential-oil diffuser instead?

If you already see a fine film on furniture, read what causes humidifier white dust and how to stop it.

Size it for the space

A humidifier has to replace the moisture that leaks out with the air, so a leaky house or an open-plan floor needs far more output than a closed bedroom. The humidifier size calculator estimates the gallons per day you need from your room, your current and target humidity and how airtight the home is. For specific models, compare the best humidifier for a bedroom, the best humidifier for a large room and, for a furnace-mounted system, the best whole house humidifier; single-model overviews cover the Levoit Superior 6000S and the Levoit OasisMist 1000S, and read how long it takes for a humidifier to work before deciding a unit is too small.

Placement

Where the humidifier sits affects how well it works and whether it leaves damp patches: off the floor, away from walls, wood furniture and electronics, and a few feet from the bed. Where to put a humidifier covers each room. Growing tropical houseplants? Thinking of adding a scent? Read about essential oils in a humidifier first: many manuals forbid it, and some oils are a concern for pets.

Water and cleaning: the part that keeps it safe

The CPSC found that bacteria and fungi often grow in humidifier tanks and can be released in the mist, and that mineral scale gives them a surface to grow on. The EPA’s routine is simple: empty, wipe dry and refill every day, and clean portable units every third day. Our step-by-step guide on how to clean a humidifier covers vinegar descaling and disinfecting, and what kind of water to use in a humidifier explains distilled vs tap vs filtered water.

Tip: If a humidifier leaves a damp patch around it, condensation on windows or a haze in the air, it’s putting out more than the room can take. Turn it down or use its humidistat.

Fix common problems

• Water on the floor: why is my humidifier leaking.
• Visible fog that hangs in the room: humidifier making the room foggy.
• No mist from an ultrasonic unit: HoMedics humidifier not misting.
• Not sure about the bedroom door: should you close the door when using a humidifier.

Babies, pets and health

For a nursery, the best humidifier for a baby covers cool-mist models, placement away from the crib and cleaning. If you have pets, read are humidifiers safe for dogs, including why essential oils don’t belong in a humidifier around animals. And for colds and stuffy noses, does a humidifier help with congestion summarizes what health sources say. A humidifier can make dry air more comfortable, but it isn’t a treatment: talk to your doctor about symptoms that don’t go away.

When the problem is too much humidity

If your hygrometer reads above 50% most of the time, you need the opposite: see how to reduce humidity in the house and condensation on windows. Not sure which way your home leans?