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Ultrasonic humidifier (left) and evaporative humidifier (right)

The Spruce / Krystal Slagle & Jorge Gamboa

The Ultimate Guide

Introduction

Ultrasonic vs. Evaporative Portable Humidifiers Comparison Guide

Learn the key differences

ultrasonic and evaporative humidifiers
Ultrasonic humidifier (left) and evaporative humidifier (right)

The Spruce / Krystal Slagle & Jorge Gamboa

If your indoor air is dry, you can add moisture into certain rooms in your home by using a portable humidifier. A humidifier may make your indoor air more comfortable and offer moisture relief for dry skin, dry sinuses, and sore throats.

Cool-mist humidifiers are safer than warm-mist models because the appliances do not involve hot or boiling water. Choose from two main types of portable cool-mist humidifiers: ultrasonic and evaporative. While either can be efficient in terms of humidifying a room, they have significant differences in how they produce that moisture. You may have to accept some trade-offs if you want to get the unit with your preferred characteristics.

Ultrasonic vs. Evaporative Humidifiers

Both ultrasonic and evaporative humidifiers serve the same function—to increase room humidity levels by adding water vapor to the air. Ultrasonic humidifiers do this by means of vibrations create by two ceramic plates, while evaporative humidifiers use a simple fan to speed up the natural process of water evaporating from a wick. Choosing between a design will depend on what features are more important to you.

Illustration of ultrasonic and evaporative humidifiers
Illustration: Ellen Chao. © The Spruce, 2019

Key Features

Ultrasonic Humidifier

An ultrasonic humidifier uses high-frequency sound vibrations to produce an extra-fine water mist that is then expelled to add moisture to the room. It's the quieter of the two types of humidifiers. The ultrasonic generally has no filter factored into its design, which saves operation costs. This type of humidifier is considered safer since there is no hot water present in the unit and therefore no risk of scalding. However, as with any humidifier that does not boil the water to produce a mist, there is a risk of bacteria being present in it and being discharged to the room. Therefore, disinfecting the humidifier becomes even more important than with a warm mist humidifier that does boil the water. 

Evaporative Humidifier

Evaporative humidifiers have been in use for decades and are considered the most common humidifying appliance. The most basic way to humidify a room is to place a pot or jar of water in the room and allow the moisture to naturally evaporate into the air to relieve dryness. An evaporative humidifier works on basically the same principle, but it uses a fan to speed up the evaporation of water and increase humidity in a room. The built-in fan draws in air that blows through a moist wick filter at the bottom of the humidifier. As the water evaporates into vapor, it's pushed out as water mist or spray into the air to increase humidity.

Appearance

Ultrasonic Humidifier

The most familiar portable ultrasonic humidifier is in the shape of a teardrop with the mist coming out from the top. There are numerous portable ultrasonic humidifier designs, including some models that have fillable tanks and others that require that you insert a water bottle. There are even mini ultrasonic humidifiers that you can place directly into a glass of water as its moisture source. Many ultrasonic humidifiers offer various additional features, such as aromatherapy, USB power, color-changing LED night lights, LED display pads, and built-in clocks.

If you're interested in a fun and decorative addition to your room, opt for an ultrasonic humidifier. Keep in mind, however, that its LED lights may keep you awake if the appliance is placed in a bedroom.

ultrasonic humidifier
The Spruce / Krystal Slagle

Evaporative Humidifier

Portable evaporative humidifiers are a bit bulkier in appearance because they need room for filters, fans, and fillable tanks. A wick filter can be quite large and takes up most of the space inside of a humidifier's casing. The type of filter used varies considerably depending on the appliance's design. With most, the filter will require routine cleaning or replacement. Some evaporative models are also designed to provide aromatherapy during the humidification process. Very few models in this category are non-filter units that simply churn out a water mist or vapor.

evaporative humidifier
The Spruce / Jorge Gamboa

Humidifier Size

Both types of portable humidifiers come as compact, tabletop, or freestanding tower floor models that are on wheels for easy mobility. What matters is choosing the correct size of humidifier for your room. Humidifiers have ratings that show what square footage they'll cover within a 24-hour period. For example, a personal compact humidifier can humidify 25 square feet (best for a desk area), but a model rated for 100 square feet would be best for a small bedroom.

If the humidifier is too large and powerful for the space, condensation will begin to form on the windows, which can result in the growth of mold, mildew, and bacteria. The bottom line: Know the square footage of the room in order to choose a humidifier that is the right size.

Whichever type you choose to buy, always monitor your humidity levels. Ideally, humidity levels in a room should be between 30 percent and 50 percent. Some humidifiers have a built-in gauge that measures the room's humidity level. Otherwise, you can test it with an inexpensive device called a hygrometer.

Care and Cleaning

Ultrasonic Humidifier

Ultrasonic humidifiers tend to produce fine grayish dust that can settle around the room, since they have no filter to absorb minerals in the water. Some models, however, come with ceramic-type cartridges that can be refreshed, and these are effective to some degree.

Ordinary tap water often contains a notable mineral content, and with no onboard filters, ultrasonic humidifiers may turn this mineral content into a fine gray or white dust that goes into the air along with the water vapor. This mineral dust lands on furniture and electronics, and it is almost impossible to avoid. The amount of dust will depend on the source of your drinking water. Hard water is notably higher in dissolved minerals that will create dust when processed through an ultrasonic humidifier. Using distilled or filtered reverse osmosis water will reduce the amount of dust you need to clean, though this can be a pricey option. If this is a major annoyance for you, consider buying a unit with a decalcification filter.

Evaporative Humidifier

The evaporative humidifier is a popular design because of the filter's function which traps mineral scale and reduces the risk of fine white/gray scale dust filtering to the room. Mineral scale dust is usually barely noticeable.

Noise

Ultrasonic Humidifier

The most common places for a portable humidifier are the bedroom or the main living space, so it's no wonder that most consumers want a humidifier with quiet operation. If humidifier noise is your main concern, an ultrasonic humidifier is your best choice. An ultrasonic humidifier does not have a fan to add to the noise of the appliance. You should recognize, though, that no humidifier is entirely silent.

Evaporative Humidifier

If noise concerns you less than expense, choose a more affordable evaporative humidifier. Sound levels vary according to design, but all evaporative humidifiers will produce a notable amount of noise due to the internal fan that runs more or less constantly.

Operation

Set up for both an ultrasonic and evaporative humidifier is relatively simple. Add water to the reservoir, position the appliance 1 to 3 feet away from walls to avoid moisture damage, plug it in, and adjust your settings. The only difference you'll have with an evaporative humidifier is the simple installation of a new filter. In terms of operation, there is no advantage of one type of humidifier over the other.

Cost

Ultrasonic Humidifier

When the technology was still new, ultrasonic humidifiers typically were considerably more expensive than evaporative humidifiers. However, with increased popularity has come increased supply, and today's ultrasonic humidifiers are only slightly more expensive than the older evaporative designs. Highly rated units designed for a moderately large room (500 square feet) can be purchased for about $75.

Evaporative Humidifier

Once costing considerably less than ultrasonic humidifiers, evaporative humidifiers today are only a little less costly than ultrasonics. A good unit designed for a moderately large room (500 square feet) will cost about $50. However, when you consider the cost of replacement filters, the cost advantage of an evaporative humidifier becomes less relevant.

Lifespan

Both ultrasonic and evaporative portable humidifiers will last two to five years if they are properly maintained. Even the best-maintained humidifiers are prone to the build-up of mineral deposits over time that can be hard to remove, and that will indicate the need for a new appliance.

The Verdict

If you loathe changing or cleaning a humidifier filter or you simply want a quieter humidifier, chose an ultrasonic filter-free model. With the increased popularity of this design, you now have many, many options when it comes to ultrasonic humidifiers. But you should expect to combat dust in the room more frequently.

For slightly lower pricing, choose an evaporative humidifier, but understand that filters need periodic changing or cleaning to keep them running efficiently. Locate filter replacements before buying a humidifier and always have a spare filter on hand.

Top Brands

  • Honeywell offers classic evaporative humidifiers that may not look as sleek and modern as others, but they are well-built and most efficient at making a room quickly comfortable.
  • Pure Enrichment offers petite, modern ultrasonic humidifiers, including the well-known water-droplet shape.
  • Essick is known for lightweight and easy to use evaporative humidifiers. They're also quiet, even when the fan is running.
  • TaoTronics makes whisper-quiet ultrasonic humidifiers with innovative features, such as models with twin nozzles that turn 360-degrees for targeted mists.