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The Ultimate Guide

Introduction

Ultrasonic vs Evaporative Portable Humidifiers Comparison Guide

Learn the key differences

Ultrasonic humidifier against wood grain background

Manueltrinidad / Getty Images 

If your indoor air is dry, you might want to add moisture into certain rooms in your home 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.

You'll find two main types of portable cool-mist humidifiers: ultrasonic and evaporative. (Cool-mist humidifiers can be safer to use than warm-mist models because the appliances do not involve hot or boiling water.) And 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 Portable Humidifier: Major Differences

There are three major differences between an ultrasonic and evaporative humidifier: Price, operation noise, and how each handles mineral scale deposits (white/grey dust). But first, you need to understand how the two types differ from one another.

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

Key Features

Ultrasonic Humidifier

An ultrasonic humidifier is one that uses high-frequency sound vibrations to produce an extra fine water mist that is then expelled to add moisture to the room. It is often considered the quieter of both types of humidifiers. The ultrasonic generally has no filter factored into its design. That does save operation costs, but it does come with a trade-off.

Some prefer this type of humidifier because it is considered safer in that there is no hot water present in the unit and therefore no risk of scalding since the unit does not heat the water in any way. 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. Disinfecting the humidifier becomes even more important than with a warm mist humidifier that does boil the water. 

Evaporative Humidifier

These humidifiers have been in use for decades and are considered the most common or garden-variety type of humidifying appliance. The most basic (traditional) 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 concept but uses a fan as a more efficient way of getting the humidity out to the room. A 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 add 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 where 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 also have bells and whistles, such as aromatherapy, USB power, color-changing LED night lights, LED display pads, and built-in clocks.

Evaporative Humidifier

Portable evaporative humidifiers are typically more straightforward and potentially a bit more bulky in appearance and that's because they need room for filters, fans, and fillable tanks. Though the word "wick" sounds very small, a wick filter can be quite large and takes up most of the room inside of a humidifier's casing.

In terms of filters, evaporative humidifiers can vary by design. There are only a few non-filter units that simply churn out a water mist or vapor, but most have filters that require a routine cleaning or replacing.

Some evaporative models are also designed for aromatherapy during the humidification process. Though you would expect the type of humidifier to be clearly identifiable on the packaging, that isn't always easy.

Best for Appearance: Ultrasonic Humidifier

If you're interested in a fun and decorative addition to your room, opt for an ultrasonic humidifier. Keep in mind that LED lights may keep you or family members awake if the appliance is placed in a bedroom, though some evaporative humidifiers also come with night lights and LED displays.

Sizes

Both types of portable humidifiers come as compact, tabletop, or freestanding tower floor models that are on wheels for easy mobility. What matters is knowing the correct size of either type of humidifier you'll need 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 (which may be best for a desk), but a model that says its moisture output will cover 400 square feet would be best for a very small bedroom.

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

Whichever type you choose to buy, always monitor your humidity levels. The best humidity level 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 tool called a hygrometer.

Repair and Maintenance

Ultrasonic Humidifier

Maintenance is more of an issue for a humidifier than repair and that's because of the white dust you'll find when using the appliance. You'll get more greyish dust around the room when operating an ultrasonic humidifier than with an evaporative because there's usually no filter to absorb mineral scale deposits. Some models, however, come with ceramic-type cartridges that can be refreshed, and these are effective to some degree.

Ultrasonic humidifiers tend to discharge more white/grey dust than evaporative humidifiers especially if they have no onboard filter pack to trap or contain those mineral deposits. The deposits are returned to the room along with the moisture, only to land on furniture and electronics as dust. It's impossible to eliminate this white dust. The mineral deposits in the water have to go somewhere. It's a little trade-off when you choose an ultrasonic humidifier.

That white/grey dust will be more extreme the harder your water is. Hard water is caused by the presence of mineral deposits in your water source and varies depending on your particular source for drinking water.

Remedies to control the humidifier white dust are: Use distilled or reverse osmosis water, though that can be pricey; a humidifier decalcification filter if there is one available for your humidifier model; or run the humidifier moisture on low to reduce the amount of dust you need to clean.

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/grey scale dust filtering to the room.

Also keep in mind that there is some compact, especially personal size evaporative humidifiers that have no filters in their design. Because the output is a smaller volume of moisture, mineral scale dust is barely noticeable, if at all.

Best for Repair and Maintenance: Evaporative Humdifier

The evaporative humidifier filter, which traps the mineral deposits, makes the difference in maintenance between the two types of humidifiers. A key thing to remember is that if a cool-mist evaporative humidifier has a filter, you will need to clean or replace it, but you shouldn't have to worry about scale dust.

Noise

Ultrasonic Humidifier

The most common place for a portable humidifier is in the bedroom; secondary is the main living space, so it's no wonder that the majority of 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.

Evaporative Humidifier

If noise is not a concern but the budget is, choose a more affordable evaporative humidifier. You should understand though that even those humidifiers that tout a quiet operation will be noisier when used on anything but low (moisture volume); it's impossible to totally eliminate the operation noise of humidifiers, especially an evaporative model, because it has an internal fan operation when in use.

Best for Noise: Ultrasonic Humidifier

While there are some with an optimum quiet operation, most ultrasonic humidifiers tend to operate quieter than other models. they're fan-free, which keeps noise levels down.

Installation

Set up for both an ultrasonic and evaporative humidifier is relatively simple. Add water to the reservoir, position the appliance one to three 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 placement of a new filter.

Cost

Ultrasonic Humidifier

An ultrasonic humidifier usually does not use filters and generally costs more to buy than an evaporative model. We say usually because some models can have an ultrasonic style of misting, yet also have some type of filter pack.

Evaporative Humidifier

An evaporative humidifier is cheaper to buy, but most have filters, usually wick style, that must be either washed or changed periodically. So a lower cost upfront is followed by more maintenance costs later, not to mention having to find the correct replacement filters. Replacement filter costs tend to vary depending on size and brand, but most are a low and reasonable cost.

Best for Cost: Tie

The initial cost of an ultrasonic humidifier is higher than an evaporative model. However, you won't need to worry about buying filters for an ultrasonic humidifier. The initial cost for an evaporative humidifier is lower than an ultrasonic model. But generally, there is the ongoing operation cost of replacement filters for evaporative humidifiers.

Lifespan

Both ultrasonic and evaporative portable humidifiers will last between two to five years if they are well maintained. Even the best-maintained humidifiers are prone to the build up of deposits over time which become 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. You'll pay more upfront and be prepared to clean around the humidifier more often.

For budget pricing, choose an evaporative humidifier, but understand that filters do 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.