How Humidifiers Work – Each of the 4 Types

humidifier releasing white mist in a room

Humidifiers are devices designed to increase indoor humidity levels by emitting moisture into the air. They work through various mechanisms, but the most common types of humidifiers operate using one of the following methods:

  • Evaporative Humidifiers: These humidifiers feature a wick or filter that absorbs water from a reservoir. A fan blows air over the wet wick, causing water to evaporate and release moisture into the surrounding air. The moisture-rich air is then expelled into the room.
  • Ultrasonic Humidifiers: Ultrasonic humidifiers use high-frequency vibrations to create a fine mist of water droplets. A small metal diaphragm vibrates at an ultrasonic frequency, breaking down water into tiny particles that are released into the air as a cool mist.
  • Steam or Warm Mist Humidifiers: These humidifiers heat water to create steam, which is then released into the room. The warm mist provides a comforting effect and can help raise indoor humidity levels quickly. However, it’s important to use caution with these humidifiers to prevent burns.
  • Impeller Humidifiers: Impeller humidifiers use a rapidly spinning disk to break up water into tiny droplets, which are then expelled into the air by a fan. They are often used in portable, small humidifiers.

Humidifiers vs Relative Humidity

The word humidifier comes from humidity. To humidify is to increase humidity. But what exactly is humidity?

Humidity is the amount of water in the air. There is absolute humidity which describes the mass of the water in the air and then there is relative humidity which is the one we use especially in HVAC.

Relative humidity is the amount of water vapor in the air, out of the total amount that the air can hold at that temperature expressed as a percentage. As you can see, relative humidity is a function of temperature.

An increase in temperature translates to an increase in relative humidity and vice versa. Simply put, hot/warm air has the potential to hold more moisture than cold air.

When is relative humidity highest? The summer. And what happens when winter kicks in? The air’s potential to hold moisture drops massively, and that is why snow falls in summer and not any other time.

It is therefore correct to say that winter air is not only cold but it is dry. Relative humidity is therefore low during winter and high during the summer?

Most people know that high humidity is bad (because it makes our bodies feel sticky and causes mold) but what they don’t know is that low humidity is just as bad. The effects of low humidity are:

  • Dry and itchy skin
  • Dry irritated eyes
  • Respiratory infections
  • Nasal congestion
  • Nose bleeding
  • Dehydration
  • Static electricity
  • Cracking wood products
  • Brittle books and artwork
  • You feel cold

The ideal indoor relative humidity is between 30% and 50%.  Usually, the best winter humidity would be between 30% and 40% while the best summer humidity would be between 40% and 50%.

However, relative humidity can drop to 25% or lower (depending on your location) during winter. With such low levels of humidity, the air in your house will just be too dry for your comfort. And that is where humidifiers come in.

A humidifier will keep releasing moisture in the indoor air so that the relative humidity is within the required range. Furnaces also tend to dry out the indoor air so humidifiers help to balance things out.

How Humidifiers Work

All humidifiers are designed to do one thing, which is to increase indoor humidity. The only difference is how they do it and their size.

As mentioned, humidifiers are either warm-mist units or cold-mist units. Apart from that, they are either categorized as central humidifiers or portable humidifiers. Let us briefly look at how they work.

Central vs Portable Humidifiers

central humidifier
Whole-house/central humidifier

Central humidifiers are also known as a whole-house humidifiers. They are built into your central heating and cooling system to humidify the whole house.

Areas which are arid in nature (usually the South Western states like Arizona and Nevada) have drier air than other areas especially during winter. Folks in such areas will most likely need a central humidifier to increase the relative humidity of their entire house.

Central humidifiers are installed close to your furnace so that it can humidifier the air before being supplied to the house. They are expensive and also cost even more to install but once installed don’t need to be cleaned daily and are also connected to the main water supply so they don’t require you to manually add the water.

Most central humidifiers are also evaporative humidifiers. Evaporative humidifiers work just like evaporative coolers, also known as swamp coolers.

The way these humidifiers work is that air is forced to pass through a wet material like a pad. As the air moves through the wet sponge, it takes in the moisture thereby increasing its humidity.

Portable humidifiers are small devices which are available either as tabletop units or consoles. As their name implies, portable humidifiers can easily be moved from one place to another.

Usually, portable humidifiers are used to humidify a single room like a bedroom or the living room. A portable humidifier would overwhelm a big house.

Apart from being easily portable, another advantage of portable humidifiers is that they are cheap and requires no installation. They however need to be cleaned regularly to prevent them from becoming a mold breeding ground.

Another disadvantage of portable humidifiers is that you need to manually (and regularly) add water to their reservoirs. These units also use distilled water and not water directly from the faucet otherwise minerals will be deposited inside.

Portable humidifiers are available either as warm-mist humidifiers or cold-mist humidifiers. Each of them have their advantages and the choice to buy any of them depends on your preference.

Warm-Mist vs Cold-Mist Humidifiers

console humidifier on a table

Warm-mist humidifiers are also called vaporizers. They have an internal heating element which heats water in a reservoir until it boils. The steam produced from the boiling water is released directly in the air.

Although some folks do it, adding essential oils or inhalants in these humidifiers (or any other humidifiers for that matter) is not recommended. Essential oils will damage the unit and will also void the warranty.

Cold mist humidifiers produce a cool mist without a source of heat. They are considered safer than warm-mist humidifiers especially for folks with kids and pets since there is no burning/scalding risk.

Most cold-mist humidifiers have a mechanical system of agitating water so that it can be broken down into tiny and light particles before being released in the air in the form of a stream of cool fog.

The following are the different types of cool-mist humidifiers:

  • Evaporative humidifiers
  • Impeller humidifiers
  • Ultrasonic humidifiers

In a nutshell there are 4 main types of humidifiers. These are vaporizers, evaporators, impeller and ultrasonic humidifiers. Let us now look at how each of them work.

1. Vaporizers

Vaporizers are also known as steam humidifiers or warm-mist humidifiers. They produce mist by heating water until it vaporizes and then the steam is cooled down before a stream of mist can be released into the air.

They basically contain an internal heating element and a water reservoir. They have a sensor (humidistat) which measures the humidity levels in the house.

When humidity drops below the set value, a signal is sent to the unit which kicks in immediately. The heating elements vaporizes the water until the humidity levels are restored to the ideal levels.

The advantage of vaporizers is that they are inexpensive. They are also quite effective but always carry the risk of scalding your skin and are therefore a danger if you have kids or pets.

2. Evaporators

These are the most common types of humidifiers. They work very well and are safe for folks with young kids and pets.

What happens when you live a bowl or pot of water outside and come back after a few hours? The level of water in the bowl will have reduced, as long as the air is drier (can take up more moisture). That is exactly how evaporative humidifiers work.

Evaporative humidifiers have a wicking filter, fan and water reservoir. The wicking filter is always drawing/absorbing water from the water reservoir so it stays moist all the time.

When the unit comes on, the fan pulls and forces dry air through the moist filter where the air evaporates the water thereby increasing the relative humidity of the house.

What I like the most about these units is that they are self-regulating. When humidity is low (air is dry), the air evaporates more water from the filter but when humidity is high, it becomes harder to evaporate the water.

3. Ultrasonic Humidifiers

Ultrasonic humidifiers use a metal diaphragm which vibrates at an ultrasonic frequency to change water into fine particles. The particles are so fine that they can be held by you indoor air for long periods of time.

If you decide to buy an ultrasonic humidifier, it is important that you use distilled water. That will prevent white dust from being deposited inside. The white dust is usually calcium mineral deposits.

Ultrasonic humidifiers are however compact and can fit in small areas.

4. Impeller Humidifiers

Impeller humidifiers use rapidly rotating discs to break down water into tiny droplets which are then released in the air in the form of a cool mist. Impeller humidifiers are among the most inexpensive cool-mist humidifiers.

Despite their low price, impeller humidifiers are noisy and the least efficient. That is something that you should consider before buying one.

Benefits of Humidifiers

Do you need a humidifier? Or rather should you buy a humidifier? The following are the benefits of humidifiers:

1. Hydrates Skin and Hair

Dry air pulls moisture from your skin leaving it dry and itchy. By installing a humidifier, your skin and hair will stay hydrated and the itch will disappear.

2. Prevents Respiratory Infections

Most virus survive in low humidity. The dry air extracts moisture from the virus making them lighter and therefore more mobile. By increasing humidity, these virus will be demobilized which helps to reduce respiratory infections, allergies and asthma.

3. You Breath Better

Dry air is known to cause nasal congestion. That is because dry air causes the nasal/sinus membrane to dry out. Naturally, the body will humidify the air before it gets to the lungs. If the body can’t do that due to a dry, it produces more mucous to help the process which causes congestion.

A dried out mucous membrane can also result in nose bleeding especially when the nose is picked of blown. By humidifying the indoor air with a humidifier, you are therefore able to prevent a dried/cracked membrane. They also help to reduce snoring.

4. Protects Eyes

Low humidity causes the dry air to pull water from the naturally moist tear film/membrane which leaves the eyes dry, irritated and exposed to bacterial infections. By having a humidifier, your eyes health will not be compromised.

5. Warms the House

I am sure you know that high humidity makes it feel hotter than it actually is. The opposite is also true.

Dry air pulls moisture from our skin which leaves the body exposed to the element and we feel cold. Restoring humidity levels to the right levels using a humidifier makes the house feel warm.

6. Wood Products Last Longer

Dry air pulls moisture from wood and wood products which make them to shrink and crack. Gaps also develop between wooden floor planks and books and artwork becomes brittle.

If you can maintain a good level of indoor humidity using a humidifier, you wood products, books and art will remain in pristine condition for longer.

7. Prevents Static Electricity

Low humidity can make you get zapped when you touch objects in the house. That is caused by static electricity which is created through friction, induction and separation.

Dry air cannot ground the static electricity unlike moist air and that is why you are zapped when humidity is low. Installing a humidifier will add moisture in the air which will conduct these charges to the ground.

Wrap Up

And basically that is how humidifiers work. If the effects of low humidity are being felt throughout your house, you should consider installing a central humidifier. However, if you only want to humidify a certain room in the house then a portable humidifier will do it.