Evaporative Versus Ultrasonic Humidifiers – What’s the Difference?

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If you’re looking to increase the humidity in your home during the dry months, then a humidifier is the perfect device for doing so. But there are many different types of humidifiers, which all work in different ways. However, most humidifiers can be placed into one of two categories: evaporative or ultrasonic.

In this article, I’ll go over the differences between evaporative and ultrasonic humidifiers– such as their working principles, health, safety, and operation concerns.

The difference between evaporative and ultrasonic humidifiers

Evaporative humidifiers work by using a fan to blow air through a wet filter that is saturated with water.

Ultrasonic humidifiers work by vibrating a ceramic disc inside a tank of water to create mist droplets.

Below I’ll go into more detail about how each humidifier works.

How evaporative and ultrasonic humidifiers work

Evaporative humidifiers work by using a fan to move air through the unit. As the air moves through the evaporative humidifier, the air flows through a wicking filter that is saturated with water. When the air passes through this filter, it picks up moisture from the filter and transfers the moisture to the air inside of your room. This is where the evaporative humidifier gets its name- the moisture is evaporated from the wicking filter into the air that is blown into your room.

Ultrasonic humidifiers work in a much different way. One or more ceramic discs are suspended inside of a tank of water. The ceramic discs vibrate at ultra-high frequencies that cause the water to form mist particles that become suspended in the air. A small fan blows these mist droplets out of the humidifier and into your room. Once the mist droplets go into your room, they eventually evaporate into the air, raising the humidity inside the room.

Humidifier health and safety

First and foremost, the health and safety of you and your household should be of utmost concern. While some types of humidifiers have clear safety advantages, they can also impact the air quality of your home in unforeseen ways.

Evaporative humidifiers do not have many safety disadvantages, since they have no heating element and they include a filter to filter out minerals from your water. The filtration will cut down on the amount of white “humidifier dust” accumulating on the surfaces inside your home.

In order to maintain the safety benefits of using an evaporative humidifier, you’ll want to ensure that you clean or change the filter regularly.

Ultrasonic humidifiers do not have a heating element so they don’t get hot. So there is no risk of burns from using an ultrasonic humidifier. For this reason, ultrasonic humidifiers are generally safe to place in an area where a child might be able to reach it.

However, there are some safety concerns stemming from the use of ultrasonic humidifiers. Since ultrasonic humidifiers don’t have filters, the dissolved minerals that are present in most tap water will go into the air that you breathe when using an ultrasonic humidifier. This is what causes the “humidifier dust” that sometimes accumulates around your home when using an ultrasonic humidifier.

For this reason, it is very important to only use distilled water in an ultrasonic humidifier. Distilled water has been treated to remove dissolved minerals. So when using distilled water in an ultrasonic humidifier, you won’t get humidifier dust or mineral dust in your home’s air.

Humidifier mold and bacteria concerns

Another health concern from the use of a humidifier is the accumulation of mold and bacteria. If left uncleaned, your humidifier will become a haven for the growth of mold, bacteria, and other organic substances.

This is particularly a concern for ultrasonic humidifiers, which do not filter or heat the water before adding moisture to your home’s air. If your ultrasonic humidifier is left uncleaned, mold and bacteria can enter the vaporized water droplets and eventually your home’s air. Be sure to clean your ultrasonic humidifier every 2-3 weeks to inhibit the growth of mold and bacteria.

Evaporative humidifiers don’t have as much of a problem with mold and bacteria. This is because they include a filter that helps to remove mold and bacteria from the water before adding moisture to the air.

No matter what kind of humidifier you end up getting, it is always important to clean your humidifier every 2-3 weeks for health, safety, and performance reasons.

Humidifier size and coverage area

The humidifier’s type is generally inconsequential to its physical size. The main factor in the size of a humidifier is the size of its tank. This means that a bigger tank = a bigger humidifier, no matter if it’s ultrasonic or evaporative.

With this in mind, you’ll want to select a humidifier according to the size of the room that you’ll be using it in.

For instance, a small ultrasonic humidifier is suitable for use in a small space such as a bedroom since it doesn’t need to cover much area.

Quick Pick: Bedroom Humidifier
Pure Enrichment Ultrasonic Humidifier

The Pure Enrichment humidifier is one of the easiest-to-use humidifiers on the market today. It has four different settings of humidification so you can dial in the right amount of humidity for your room. When running, it is so quiet that you won't even notice that it's on.

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On the flip side, a large evaporative humidifier is more suitable for use in a large, open space such as a living room.

Generally, evaporative humidifiers are better suited for larger spaces since they use a fan to induce airflow through the humidifier unit. This means that an evaporative humidifier will usually be able to disperse moisture throughout a larger area since it has a fan to aid it in doing so. 

However, this is not always true – there are definitely large ultrasonic humidifiers and small evaporative humidifiers out there on the market that are capable of doing their jobs effectively. Just be sure to select a humidifier that is the correct size for your application.

Quick Pick: Humidifier for Large Rooms
Vornado Evap40 Evaporative Humidifier

A large 4-gallon tank makes this humidifier perfectly suited for large spaces such as living rooms. It also has a humidistat for precise humidity level control.

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Noise from ultrasonic and evaporative humidifiers

Both evaporative and ultrasonic humidifiers produce audible noises when in use. Where they differ is in the amount and type of noises that they produce.

Ultrasonic humidifiers produce a slight high-pitched “humming” noise when they are on. This humming noise comes from the vibration of piezoelectric discs to produce water droplets that add moisture to the air. 

The humming sound from an ultrasonic humidifier is barely audible to most people. Chances are that you won’t even notice the slight hum from an ultrasonic humidifier. Those that do are usually not disturbed by it. However, people with sensitive hearing might get annoyed by the noise produced by an ultrasonic humidifier.

All Evaporative humidifiers emit a considerable amount of noise from the fan that blows air through the unit. The fan in an evaporative humidifier generally generates much more noise than an ultrasonic humidifier does. For this reason, light sleepers should stay away from using evaporative humidifiers in their bedrooms.

Pricing and operation costs

Owning a humidifier comes with costs, both upfront costs, and costs associated with the continued operation and maintenance of the humidifier.

Generally, ultrasonic humidifiers have a larger upfront cost, while evaporative humidifiers have greater operating costs.

Ultrasonic humidifiers usually cost a little bit more to purchase. This is because their working principle is a little more complicated and requires more parts to work. However, once you own an ultrasonic humidifier, you won’t need to buy and replace any filters. However, you’ll want to take into account the costs of using distilled water since most ultrasonic humidifiers require you to use distilled water to work effectively.

Evaporative humidifiers are usually a bit cheaper upfront. However, in order to keep your evaporative humidifier running safely and effectively, you’ll need to replace or clean the filter according to the manufacturer’s recommendations. Generally, you should be replacing your humidifier’s filter every 1-3 months.

Air contaminants will reduce your humidifier filter’s lifespan. As your evaporative humidifier operates, it pulls in air from your home to add moisture to it. When your humidifier brings in air, it can pull in dust, smoke, and other air particles. These particles get trapped in the filter, and over time the filter will become embedded with particles that hinder its performance.

Both types of humidifiers require cleaning every 1-2 weeks. No matter if you have an ultrasonic or evaporative humidifier, you’ll want to empty out its tank and clean its parts every 1-2 weeks. If your home is dusty, has pets, or smoke, then you’ll want to clean your humidifier more often. 

Features – Ultrasonic versus evaporative humidifiers

Both types of humidifiers come with extra features that go beyond the simple task of adding moisture to your air. Below, I’ll go over a few of the additional features that many humidifiers include:

  • Aromatherapy. Many ultrasonic humidifiers include an aromatherapy tray that allow you to add your favorite aromatherapy treatment or essential oils for dispersion into your home’s air. This feature is usually found only in ultrasonic humidifiers because they are able to safely add aromatherapy oils to the air without damaging the humidifier.

  • Light. Compact humidifiers that are designed to be put in small rooms such as bathrooms or bedrooms sometimes come equipped with an LED light embedded onto its front panel. This is a handy feature to have as a night light or reading light when it’s dark.

  • Humidistat. Some of the more expensive humidifiers come equipped with a built-in humidistat. The humidistat allows you to dial in the precise level of relative humidity that you desire in your space. After setting the humidistat to your desired level, the humidifier will cycle on and off to maintain the humidity level that you set it to.

Moisture buildup from humidifiers

One final thing to remember when selecting your humidifier is that it can cause excessive moisture buildup inside your space. This is usually seen on the inside of windows or other cold surfaces inside your home.

Excessive humidity and moisture buildup happens when the warm, moist air inside your home comes into contact with a cold surface. The cold surface forces water to condensate out of the air, and form as droplets on the cold surface.

There is no sure-fire way to prevent moisture and condensation from occurring inside your home while using a humidifier.

One thing that you can try is to ensure that your windows or surfaces are properly sealed and insulated so that they don’t get too cold. Another thing to try is to dial back the humidification level on your humidifier, so you don’t add as much moisture to the air in the first place.

Ultrasonic humidifier moisture buildup

Ultrasonic humidifiers can sometimes cause moisture buildup on the surface that they sit on. This usually happens when an ultrasonic humidifier is placed on the floor or a large table.

The reason that this happens is that the water mist particles do not have enough time to evaporate into the air after being dispersed out of the ultrasonic humidifier. After the mist is dispersed, it slowly falls down through the air and then rests on the surface around it, causing water droplets to build up.

To prevent this, put your ultrasonic humidifier on a higher surface such as a shelf or countertop. Be sure that there is enough open space around your humidifier (especially the top) to allow the water droplets to properly disperse into the air surrounding it. 

If you are seeing moisture buildup around your ultrasonic humidifier, this could also be an indication that there is not enough airflow in your room to allow for the water mist particles to properly disperse throughout your room. Consider using a fan to circulate the air in your room to help prevent this from happening.

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