Ultrasonic Vs Evaporative Humidifiers: Which Is Best To Buy?

Ile Kauppila

Written By

Ile Kauppila

Expert Reviewed By

Josh Mitchell

Last Updated On

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I’ve had a lot of people ask me what the differences between evaporative and ultrasonic humidifiers are. I can’t blame them — they both seem very similar, after all.

Both types of humidifiers boost humidity levels by producing cool water vapor.

That’s where the similarities end, though, and the units have significantly different pros and cons.

If you’re not sure which humidifier is right for you, don’t worry.

In this guide, I will explain ultrasonic and evaporative humidifiers to help you make an informed choice!

Key Takeaways

  • Ultrasonic humidifiers add moisture to the add by turning water into tiny droplets through ultrasonic sound vibrations. They are silent and portable.
  • Evaporative humidifiers use a fan blowing over a wet-wicking filter to add moisture to the air. They are louder.
  • Evaporative humidifiers use a filter to catch some impurities. Ultrasonic units do not have any filters at all.

Key Differences Explained For Ultrasonic & Evaporative Humidifiers

ultrasonic vs evaporative humidifiers

Warm Vs. Cool Mist Options

Evaporative and ultrasonic humidifiers are both cool mist humidifiers.

Neither machine relies on a heating element to produce water vapor.
Types of humidifiers

I like them because I don’t have to worry about burns or hot water spills!

There are some specialized ultrasonic humidifiers that can heat up the water vapor.

I strongly recommend purchasing a dedicated warm mist humidifier, though.

Warm mist humidifiers are specifically designed for boiling water and producing hot steam to increase the humidity levels in your home and often work better than these hybrid units.

TL;DR: Ultrasonic and Evaporative humidifier do not boil water to produce vapor and hence are categorized as cool mist humidifiers.

Noise Levels Vary

Evaporative humidifiers are louder than ultrasonic ones.

Most evaporative humidifiers use a fan to disperse moisture, which results in noise.

An ultrasonic humidifier only uses two quietly vibrating plates to push water droplets into the air.

It’s almost completely silent, which is why I like keeping an ultrasonic humidifier in my bedroom.

TL;DR: Ultrasonic humidifiers are quieter.

Both Are Generally Safe To Use

In general, both ultrasonic and evaporative humidifiers are safe devices to operate. 

They don’t have hot parts, so there is no risk of fire hazards or burns.

However, both require regular cleaning and maintenance to avoid harmful mold or bacterial growth and to ensure good indoor air quality.

Additionally, spills or leaks could lead to water damage, so I recommend placing the humidifiers at least three feet away from other objects and common areas of traffic.

TL;DR: Both are relatively, but beware of correct placement to avoid spills and dampness that can become breeding ground for mold.

Both Are Ideal For Children’s Room

A cool mist humidifier — whether evaporative or ultrasonic — is an ideal choice for adding moisture to a nursery or a child’s bedroom.

They are small and portable humidifiers, so you can easily place them out of the reach of small hands.

They also don’t have any hot parts, so both evaporative humidifiers and ultrasonic humidifiers are much safer around children.

I strongly recommend going for one of these units instead of a warm mist humidifier if you plan to use it in your child’s room.

However, ultrasonic humidifiers are unfiltered, which may prove to be an issue if your child is allergic. In that case, I recommend opting for an evaporative device.

TL;DR: Evaporative humidifiers have a slight edge due to presence of a filter.

Ultrasonic Humidifiers Offer Better Aesthetic Appeal

Beauty is always in the eye of the beholder, but many people (me included) find ultrasonic humidifiers more pleasant to look at than evaporative ones.

They’re less bulky, so it may be easier to make the humidifier disappear among your furniture and decorations.

There are many different available models for both machines, though, so you can likely find one that blends into your home.

TL;DR: While beauty if subjective; ultrasonic do take the cake in most eyes.

Ultrasonic Type Are Smaller And Less Bulky

An ultrasonic humidifier is nearly always smaller than an evaporative one.

An evaporative humidifier must have room for the wick filter, fan, and water tank, which tends to make them larger.

You can find both devices in many different sizes, but there are definitely general trends.

Evaporative Humidifiers Promote Cleaner Air

An evaporative humidifier can contribute more to clean indoor air than an ultrasonic one.

Evaporative machines feature a wick filter, which can bind allergens, bacteria, and other air pollutants.

Ultrasonic humidifiers don’t have filters, so they will spew any possible contaminants in the water into your home.

Important Note:

While evaporative humidifiers have filters, they are not a replacement for air purifiers. Neither humidifier is designed to remove pollutants or allergens from the air.

If you’re looking to maintain air quality in your home by cleaning it, I say purchase a whole-house air purifier instead.

Ultrasonic May Disperse Mineral Deposits If Water Unfiltered

As it includes a wick filter, I recommend an evaporative humidifier if you live in an area with hard water.

The filter removes minerals dissolved in water and keeps them out of your indoor air.

However, the filter will quickly develop mineral deposits, so you must change the humidifier’s filter regularly.

An ultrasonic humidifier will disperse minerals in the water to your home.

This can result in fine mineral dust settling on your home’s surfaces, which can potentially cause allergic reactions.

Distilled water for humidifiers

The dust did a number on my breathing, so I recommend always using demineralized water instead of tap water in an ultrasonic humidifier — or any humidifier, for that matter. (1)

TL;DR: Ultrasonic humidifiers are more susceptible to issues arising from wrong choice of water. Always aim to use distilled water for any type of humidifier.

Evaporative Humidifier Is Relatively Higher Maintenance

An evaporative humidifier requires more maintenance than an ultrasonic humidifier.

Evaporative models require wick or filter replacements, which adds to the running costs and effort of maintenance.

how often to change evaporative humidifier filters

Both types of humidifiers need regular and thorough cleaning, though.

I advise you to wash the fillable tanks once a day with water and white vinegar to avoid the risks of mold or bacterial buildup (more on that a bit later).

Ultrasonic Humidifiers Are More Portable

Ultrasonic humidifiers are generally more portable than evaporative due to their smaller size and lower weight.

If you will be humidifying specific rooms only occasionally, an ultrasonic humidifier is easier to move around and store.

Evaporative humidifiers can come in smaller designs but they might be too small to effectively maintain acceptable humidity levels.

I always go for an ultrasonic unit when portability matters

TL;DR: While both come in different sizes, ultrasonic are generally smaller, lighter and thus more portable.

Ultrasonic Humidifiers Are Generally More Expensive

When it comes to the initial purchase, ultrasonic humidifiers tend to be more expensive.

Their operational mechanism is more complex, which pushes up their price. If you’re looking for low up-front costs, pick an evaporative humidifier.

Ultrasonic Models Are Cheaper To Operate

Although ultrasonic humidifiers cost more at the store, they come with fewer running costs as there is no humidifier filter to replace.

In addition, ultrasonic humidifiers tend to consume very little electricity — which I really like.

Unlike their ultrasonic counterparts, evaporative humidifiers require you to change the filter regularly to maintain device effectiveness and cleanliness.

Filter maintenance and higher power consumption make these devices more expensive to maintain.

TL;DR: Ultrasonic humidifiers are expensive to procure but cheaper to operate. The reverse is true for evaporative humidifiers.

Both Types Carry Risks

Both types of humidifiers run the risk of growing bacteria and mold that can aggravate your lungs and even cause respiratory infections. They need regular cleaning to avoid this risk.

Additionally, both machines can raise the humidity levels in your home too high above the recommended 30-50% humidity. (2)

That much moisture contributes to the growth of mold and dust mites (as I found out the hard way with my first unit).

Important Note:

It’s best to invest in a model with a built-in humidistat to prevent excessively humid air.

Since they both use water, ultrasonic and evaporative humidifiers can leak or spill.

They could damage water-sensitive valuables or surfaces, so keep them on safe, steady desks or tables.

An ultrasonic humidifier has no filters, so it runs the additional risk of introducing harmful pollutants to indoor air if they’re present in the water.

Instead of tap water, you should use purified or distilled water in an ultrasonic humidifier.

TL;DR: Mold growth, water damage to objects, and health issues caused by over humidification are risks both evaporative and ultrasonic humidifiers carry. These can be mitigated with following proper usage and placement guidelines.

Comparing An Ultrasonic Versus Evaporative Humidifier For A Baby

humidifier placement in nursery

Humidifiers can alleviate cold and flu symptoms in babies.

As ultrasonic and evaporative models are both cool mist humidifiers without dangerous hot parts, they’re great for safely adding moisture to your baby’s room to relieve coughing, dry skin, or allergies.

However, evaporative humidifiers have a wicking filter that does a decent job of removing minerals and possible pollutants from water.

As such, I generally recommend an evaporative humidifier for a sensitive or sick child.

If you choose an ultrasonic model, a layer of white dust can coat the child’s room due to the mineral content in the water.

Additionally, they won’t filter out any water-borne impurities and risk introducing air pollutants to the room.

As I already mentioned, always use distilled water in an ultrasonic humidifier, especially in your child’s bedroom. I really can’t stress that enough.

TL;DR: Evaporative humidifiers have a wick filter that have the added benefit of promoting cleaner air making it the better option for a baby's room.

How Do Ultrasonic Humidifiers Work?

How does an ultrasound humidifier work

An ultrasonic humidifier has a ceramic or metal plate or plates, called a diaphragm, underneath a water basin.

The machine vibrates the diaphragm at an extremely high frequency to separate the water into microscopic water droplets.

It then disperses the droplets to the room to add moisture to the air.

The vibrations of the plate are too high frequency for human hearing, so an ultrasonic humidifier is mostly silent.

At most, it emits a faint hissing sound as the humidifier releases water droplets into the room. I actually find my bedroom humidifier’s quiet hiss very soothing.

Pros & Cons Of Ultrasonic Humidifiers

Pros
  • Small size: Due to their small form factor and simple design, ultrasonic humidifiers take up little space.
  • Safety: These devices work with cool water, so there are no heating elements. This may be safer in a home with small children or pets.
  • Low running costs: Ultrasonic humidifiers are cheap to operate after the initial purchase.
  • Less maintenance: You don’t need to change any filter or wick, so these machines only need regular cleaning.
  • Low electricity consumption: Ultrasonic humidifiers consume little power and won’t add much to your electricity bill.
  • Silent operation: The vibration frequency is beyond the level of human hearing. This makes an ultrasonic device a quieter humidifier and better for a bedroom.
CONS
  • Water condensation: Ultrasonic humidifiers release water in droplets, which can settle outside the humidifier before evaporating.
  • Minerals: With hard water, excess minerals can be released into the air, which can dry out and create white dust.
  • Less hygienic: There is no filter, so biological or allergenic contaminants could be released into the air.
  • Over-humidification: Ultrasonic units are highly efficient and could cause over-humidified air. To prevent excess mold growth from too much humidity, I recommend buying a hygrometer to detect humidity levels.

How Do Evaporative Humidifiers Work?

An evaporative humidifier works with a wicking filter and a fan. The wick draws water out from the water reservoir to dampen itself.

The evaporative humidifier then uses a fan to blow cool air over the filter to evaporate the water, increasing humidity levels in the room.

Important Note:

There are also other evaporative humidifiers called natural evaporative humidifiers, which don’t feature a fan. These devices rely on natural evaporation, which makes them quieter than their fan-powered counterparts.

A natural evaporative humidifier is slower to work and may not be as efficient. However, I really like the quiet operation and lower running costs.

Pros & Cons Of Evaporative Humidifiers

Pros
  • Natural vapor: Evaporative humidifiers release fine water vapor, so there’s less risk of condensation.
  • More hygienic: The internal wick or filter removes pollutants from the water before it evaporates, reducing the chance of emitting bacterial or allergenic contaminants.
  • Softer water: The wick will draw out some excess minerals in hard water, releasing softer water into your room.
  • Lower water consumption: Some evaporative models can draw in excess moisture from the air to be recycled in the basin.
CONS
  • Bigger size: Evaporative humidifiers tend to be rather bulky, which can limit your options when placing them.
  • Maintenance: The wick filter needs regular changing to avoid mineral or bacterial contamination.
  • High running costs: Although the initial price is low, evaporative humidifiers need replacement filters and consume more electricity.
  • Noise: The humidifier’s running fan can be fairly loud, which might not be ideal for a bedroom or living room.

Common Questions Asked (FAQ)

Does A Cool Mist Humidifier Make The Room Colder?

A cool mist humidifier will not decrease the temperature of the room it’s placed in.

In fact, it can make you feel warmer as a high moisture content in the air can help you retain body heat.

Can I Use Filtered Water Instead Of Distilled Water?

You can use filtered water in your cool mist humidifier if you live in an area with soft water.

However, filtering doesn’t remove excess minerals dissolved in the water, so in a region with harder water, it’s smart to stick to distilled water or demineralized water.

Do Cool Mist Humidifiers Help Sinuses?

Cool mist humidifiers can alleviate sinus related issues.

By adding humidity to the air, they can relieve congestion in your sinuses, open up the nasal passages, and let breathe easier.

Does A Humidifier Help With Coughs And Phlegm?

Yes, humidifiers offer relief for coughing and excess phlegm.

Dry air can irritate your airway, which makes you cough, and your body produces mucus to moisten your membranes.

Humidified air moisturizes these surfaces and reduces coughing and mucus congestion.

Where Should I Place A Humidifier?

You should place your humidifier in a central location at least three feet away from people and moisture-sensitive objects.

For more tips, read my guide on where to put your humidifier.

Who Takes The Cake?

So, who wins — an ultrasonic or evaporative humidifier? It all depends on what you’re looking for.

I prefer ultrasonic humidifiers. These quiet, portable humidifiers are awesome at adding moisture to bedroom air.

However, an evaporative humidifier is less likely to introduce mineral dust or bacteria to your living space.

With my guide, you can make the right choice between ultrasonic vs. evaporative humidifiers. Whichever you choose, you’ll be on your way to breathing easier with well-humidified indoor air!

References: 

  1. https://www.epa.gov/sites/default/files/2014-08/documents/humidifier_factsheet.pdf
  2. https://health.clevelandclinic.org/how-you-can-tell-if-you-need-a-humidifier/
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Ile Kauppila

MA Multimedia Journalism / BA English Philology

Ile Kauppila
Ile Kauppila is a globetrotting writer and editor living in Virginia. Ile holds an MA degree in Multimedia Journalism and a BA in English Philology. Ile has written for a variety of home, HVAC, and energy-related websites and publications. He has covered HVAC solutions, insulation, and energy-efficient construction, automotive AC systems for multiple auto dealerships and garages.

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