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Ultrasonic and Evaporative Humidifiers Comparison

Updated on February 6, 2013
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Susette has a practical, lifelong interest in good physical & mental health, including the environment that sustains us all.

A hygrometer measures moisture in the air.
A hygrometer measures moisture in the air. | Source

When the air gets too dry in a person's house, it can cause a number of discomforts, especially in winter with central heating and in summer with the air conditioning. I wake up in the morning often with a very dry throat and dry eyes. Neither does my skin like it dry. And my plants get parched and brown along the edges or tips, unless I mist them a few times a day.

One day I noticed how nice it felt walking through the mist I was creating for my plants. I began to wonder what it would be like to have a humidifier in my house and what kind might be best. This article is the result of that research.

What Do Humidifiers Do?

Humidifiers are machines that spray mist into the air, using different methods to counteract the drying effect of heaters and air conditioners, while keeping the air at a controlled and comfortable humidity for humans. (If static electricity is present, then the air is too dry.) The right humidifier can help relieve asthma, cold and flu, bronchitis, nosebleeds, dry throat and chapped lips, sinus allergies, and skin problems. It can disinfect airborne diseases, prevent wood furniture and floors from drying out, and can help the leaves of your indoor plants stay green.

You can get humidifers in different sizes and different technologies. There's a large size for the whole house, medium sizes for single rooms, and smaller sizes to carry around. Some humidifiers produce a cool mist, others a warm mist. The different kinds use more or less or no electricity. Most look like functional machines, while some are decorative.

The two most highly recommended technologies are ultrasonic and evaporative room humidifiers. Both produce a cool, rather than warm mist in the air. Both are electric and easy to set up. I have described them in some detail below, and have listed some of the other alternatives near the end.


Ultrasonic Humidifiers

This technology works by ultrasonic sound waves that induce water held in a reservoir to make fine droplets that rise silently up into the air as mist. This fine mist - only 1 micrometer in diameter - is blown out into the room as a light fog, blowing out with it any metals or bacteria that were in the water. This is the most efficient method of misting, but also the most costly.

Humidifier Maintenance & Filters

Maintenance is always a factor when you purchase a machine to do a job. Here are the main steps you will need to take to keep this kind of humidifier functioning well:

  • Clean the water reservoir daily to prevent any bacterial buildup. Unplug unit, empty tank, wipe all surfaces dry, and refill water (per EPA - see article below).

  • Use distilled, rather than tap water to fill the reservoir. Any minerals in tap water will otherwise be sprayed out into the room, causing a white powder residue buildup on your furniture.

  • For those humidifiers that use filters or demineralization cartridges, be sure to replace it whenever there's buildup.

Comparative Benefits & Detriments

Both the ultrasonic and evaporative humidifiers do a good job of moistening the air, however there are some differences, which may or may not be important to you. You will want to weigh carefully the relative benefits and detriments of each type before purchasing, comparing them also with your own health stamina and priorities of daily living.

  • Mist production with this technology is much quieter than with the other.

  • Any bacteria and minerals existing in the reservoir water are distributed throughout the room, along with the mist, when you use tap water with this kind of humidifier.

  • The humidifier needs to be cleaned daily.

  • It costs more to buy.

Evaporative Humidifiers

This kind of humidifier is also known as a wick humidifier. The wick is a filter that absorbs water like a sponge, providing a larger surface area from which water can evaporate. Air blown across the wick by a fan in the humidifier creates a cool mist of evaporated water that quickly raises humidity in a room to a comfortable level. It's a self regulating system - if the room is already humid, then not much water will evaporate, whereas a dry room induces a high evaporation rate.

How They Work

Humidifier Maintenance - Filters

  • The wick filter needs to dry out between applications, in order to prevent mold from taking root. Try flipping it periodically to keep part of it wet and the other dry, while keeping the whole think still absorbent.

  • Any minerals in the water will accumulate in the wick and block the air flow, so change the filter regularly.

  • Once the season is over, clean the humidifier thoroughly and throw out the wick. Store in a dry location.

  • When it's time to pull it out again for use, be sure to clean off all dust first. Install a new wick.

Comparative Benefits & Detriments

  • Less apt to disperse bacteria and minerals than ultrasonic.

  • Can add air purifiers, like eucalyptus oil.

  • Doesn't need to be cleaned as often.

  • Has a wick/filter that needs replacement regularly, so maintenance costs are higher.

Cautions About Humidifiers

Here are several items to be aware of when you operate a humidifier. They can make the difference between whether having one works for you or not. Your health/resistance to disease, the time you have for maintenance, and even the kind of furniture you have make a difference.

  • Larger rooms require bigger units.

  • Too much humidity can warp wood furniture and flooring over time. It can also breed dust mites, which cause a different kind of allergy. Condensation on the windows is a good indication that there is too much. Keep humidity levels under 50%.

How to Clean a Humidifier

  • Keep the humidifier clean. Forgetting to change filters or clean the humidifier base can result in bacterial buildup being blown all over the house.
  • Use distilled water to fill reservoirs. This will prevent buildup of scale and other elements contained in undistilled water that can block pipes.
  • Keep absorbent materials around humidifier dry. If they get damp, turn the humidifier down or use it less often.
  • Also note that if you are purchasing an air conditioner for your home and you want a humidifier too, buying an evaporative cooler will satisfy both needs.

Buying a Humidifier

When purchasing a humidifier, there are several things to look for that will likely bug you later, if they are absent. According to reviews on and comments from other articles on humidifiers, these are the most sought-after characteristics:

  • Noise level - you want it quiet.

  • Humidity meter - assures you're not over-misting (or purchase a separate hygrometer).

  • Large water tank - it can be troublesome to have to be constantly refilling the tank.

  • Water level indicator - to make sure you don't let it run dry.

  • Automatic shutoff - for when the water reservoir runs dry and/or to conserve electricity.

  • Ease of cleaning - you don't want to have to fight the machine to get a filter or reservoir out each time.

  • Filter lifetime - Can you rinse it out to increase the lifetime? Can you flip it over? I saw one unit that has a 3 year lifetime for its filters. How does the one you're looking at compare?

Other Types of Humidifiers

Steam - Boils water inside steamer reservoir, releasing warm steam into the air. Boiling process disinfects airborne bacteria. Can burn if vaporizer is accidentally brushed against or water spilled.

Impeller - Spins mini water droplets as cool mist out into the room via a rotating disk.

Whole house - This is a forced-air humidifier that uses your central heating and air conditioning ducts to distribute the mist. It uses a different technology than room humidifiers. For this one it's imperative that ducts and filters be cleaned regularly.

Portable - Comes in a case. Small enough to carry around with you wherever you go.

Non-electric - Works by normal heat evaporation. Same effect as having healthy plants in the room.

USB humidifier - Plugs into your computer to mist the area around which you work.

Baby - Made specifically for nurseries and children's rooms. Designs in cute animal and sports shapes. Makes a unique baby shower gift.

Portable Humidifier

Natural Humidifiers

It is possible to make your own "natural" (non-electric) evaporative humidifier with standard home equipment. Here is how:

Partially fill a wide-brimmed stainless steel bowl with water. Put a towel across it with a weight of some kind in the middle. The weight will make the towel sink into the water, which will absorb water, spreading up until the whole towel is wet. The dryness of the room will cause the water to evaporate, thereby moistening the air.

As an alternative, if you already have a tower fan (where the fan itself is well protected) you can hang a wet towel over the tower and accomplish the same purpose. This is what I'm doing now, as a test, before spending money for a manufactured unit.


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    • Ericdierker profile image

      Eric Dierker 4 years ago from Spring Valley, CA. U.S.A.

      Fantastic hub, Here in the southwest it is imperative to have one. I will follow this in getting an upgrade.

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