Evaporative vs ultrasonic humidifier

Last checked 2026-10-03.

An ultrasonic humidifier turns tank water into a fine mist, so whatever is in the water, including minerals and microorganisms, can go into the air; an evaporative humidifier passes air over a wet wick, and its maker says impurities stay in the wick. That is why the two ultrasonic makers here recommend distilled or purified water, while Blueair says clean tap water is fine in its evaporative DreamWell.

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What each type asks of you

• Ultrasonic (Levoit Classic 160, Dreo HM311): the EPA says ultrasonic and impeller units can disperse minerals and microorganisms from their tanks. Dreo's manual recommends purified or distilled water "to prevent white powder residue from forming" and advises against tap water; Levoit recommends purified or distilled water and cleaning every 3 days.
• Evaporative (Blueair DreamWell H38i): per Blueair's manual, tap water is safe and visible residue collects in the wick, which is machine-washed every 1 to 2 weeks and replaced every 12 months. The wick is the running cost ultrasonic models do not have.

Mist output is not stated in any of the three manuals, so this page does not compare how much water each puts into the air.

Care that applies to every humidifier

From the EPA's Use and Care of Home Humidifiers (read 2026-10-03):

• Ultrasonic and impeller ("cool mist") humidifiers can disperse microorganisms and minerals from their water tanks into indoor air, so their care matters most.
• Use water with low mineral content, such as distilled water, to avoid releasing minerals into the air.
• Empty the tank, wipe it dry and refill it daily; clean portable humidifiers every third day.
• Do not humidify above 50% relative humidity: wetter air encourages dust mites and mold. A hygrometer shows the level.
• Steam (warm-mist) units can cause burns; keep them out of children's reach. None of the three models here is a steam unit.

The EPA's mold guide (Mold, Moisture and Your Home) puts the ideal indoor range at 30 to 50 percent relative humidity. Where each maker's own instructions differ from this, the table shows the maker's words.

Kinds of claim on this page: the EPA guidance and the cited studies are product evidence in the sense of an independent source; tank, type, water, cleaning, placement and warranty are each maker's manual statement, a manufacturer claim; anything the manual does not state, including every model's mist output rate, is unknown and shown as not stated. Recall check: the CPSC recall database on 2026-10-03 (CPSC recall database (saferproducts.gov recall API): product name 'humidifier' (30 recalls), and product name and recall title 'Levoit', 'Dreo' and 'Blueair'); none of the 30 humidifier recalls names Levoit, Dreo or Blueair, and the brand queries return none. That is not proof of safety: check your unit's model number.

Left out, and why

• Levoit NeoClassic 450 (LUH-N451-WUS): no maker manual found, and this pilot takes model facts only from manuals
• Dreo DR-HHM006: a second Dreo ultrasonic model adds no comparison
• Canopy Bedside evaporative humidifier: the Amazon offer is sold by the brand, not Amazon.com; this pilot links Amazon.com offers only

We tested nothing: no humidity, output, noise or white-dust measurements. Nothing here says a humidifier treats dry skin, allergies, colds or any condition, and a maker's room-size figure is not independent evidence of what suits your room.

More on humidifiers: Levoit vs Dreo vs Blueair, does a humidifier help dry skin?. Too humid instead: dehumidifiers.