Cool Mist vs Warm Mist Humidifiers: Which One Should You Buy?

Cool mist vs warm mist at a glance

Based on EPA's "Use and Care of Home Humidifiers" and CHOP's guidance.

	Cool mist	Warm mist
How it works	Ultrasonic vibration, impeller, or evaporation from a wick	A heating element boils water to steam (EPA calls warm mist a type of steam vaporizer)
Burn risk	None from the water	Steam and boiling water may cause burns (EPA)
Around children	Recommended by the AAP, per CHOP	Keep out of reach of children (EPA)
White dust	Ultrasonic and impeller: yes with tap water; evaporative: not expected	Not expected (EPA)
Power use	Lower; no heating	Higher; boiling water takes energy
Noise	Ultrasonic: very quiet; evaporative: fan	Varies by model
Ongoing cost	Distilled water (ultrasonic) or wicks (evaporative)	Electricity; descaling the heater

Difference 1: safety

This is the deciding factor in most homes. EPA's humidifier guidance says steam and boiling water may cause burns and that steam vaporizers should be kept out of the reach of children. CHOP's guidance cites the AAP's recommendation of a cool mist humidifier and explains that vaporizers can burn a child who gets too close to the steam or knocks over a unit full of hot water. CHOP also suggests keeping any humidifier about 3 feet from a child's bed or crib. Pets that knock things over are a similar concern.

Difference 2: white dust and minerals

EPA says ultrasonic and impeller units are very efficient at dispersing minerals in tap water into the air, which can settle as white dust, while steam vaporizer and evaporative units are not expected to disperse substantial amounts. So "cool mist" is not one thing: an ultrasonic cool mist unit needs distilled water to avoid white dust, but an evaporative cool mist unit does not. If you have hard water and want cool mist, choose evaporative. See ultrasonic vs evaporative.

Difference 3: power and running cost

Heating water to steam takes far more energy than vibrating it into mist or evaporating it with a fan. A cool evaporative unit like the Vornado EVDC500 can draw as little as 1 watt in its low-power mode, according to Vornado, and a cool ultrasonic like the Levoit Classic 200 is rated at 24 watts. Warm mist models need a heating element on top of that. If you run a humidifier all winter, the difference shows on the bill.

Difference 4: comfort

Warm mist feels warmer at the outlet, which some adults like in a cold room, but a humidifier is not a heater. Both types add the same thing to the air, water vapor, and what matters for comfort is the room reaching 30 to 50% humidity, the range EPA recommends. See the ideal indoor humidity level.

Difference 5: cleaning

EPA advises emptying, drying and refilling portable units daily and cleaning them every third day, following the maker's instructions; without them, it suggests 3% hydrogen peroxide on surfaces that touch water. The boiling in a warm mist unit does not replace cleaning: minerals scale the heating chamber and need regular descaling, and the reservoir can still grow microbes between uses. CHOP suggests cleaning every 2 to 3 days of use. See humidifier mold prevention.

Our picks

From each maker's page or manual; LV600S per its Amazon listing.

Humidifier	Mist	Type	Tank	Best for
Honeywell HCM-350	Cool	Evaporative	1.1 gal	Children's rooms, hard water
Pure Enrichment MistAire	Cool	Ultrasonic	1.7 L	Small rooms on a budget, with distilled water
Vornado EVDC500	Cool	Evaporative	2 gal	Living rooms, low power
Levoit LV600S	Warm or cool	Ultrasonic with heater	6 L	Adults who want warm mist in winter

Who should buy which

• Cool mist if there are children or pets in the home, if you want lower running costs, or if the unit goes in a nursery. Choose evaporative for hard water; see baby humidifier safety.
• Warm mist if it is for adults only, it sits where no one can knock it over, and you prefer warm output.
• A warm-and-cool unit if you want warm mist in an adult bedroom and the option of cool mist elsewhere.

For ranked picks across all types, see the best humidifiers. For the difference between a humidifier and a steam vaporizer used for colds, see humidifier vs vaporizer.