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What is a Humidifier?

A humidifier adds water vapor to the air to increase humidity.

How a Humidifier Works

During the cold winter months, you might focus most of your efforts to stay comfortable indoors on your heating system. But as the temperature drops, don’t forget about your humidity levels to help ensure you’re comfortable in your home. As we bring in outside air and heat it, the humidity levels drop substantially. When humidity levels are off, both you and your home may feel the effects.

One of the best ways to regulate humidity levels is by investing in a humidifier. Humidifiers add moisture to the air in your home to reach optimal humidity levels, which in turn can improve the overall air quality inside. Here, we’re going over what you need to know about these systems — from how they work to the different types available — so you can choose the humidifier that works best for your home and budget.

What is a humidifier?

A humidifier adds moisture to the air in your home, with the end goal of optimizing indoor humidity levels. The term “humidity” simply refers to moisture in the air. The term relative humidity is the percentage of moisture in the air compared to what the air can hold at a given temperature. The optimal indoor humidity level is typically between 30% and 50%, according to the EPA, which means it’s best to have air containing between 30% and 50% relative humidity in your home.

When humidity levels are lower than this range, you might be met with physical issues like dry skin, static shocks, or sinus infections, while in your home you may notice cracking wood or chipped paint. When humidity levels are higher than this range, it may trigger health concerns like asthma or restless sleep, and you might notice an increase of mold growth in your home.

A humidifier works to reduce these problems by regulating the humidity levels in your home to keep them within that optimal range, and the best ones do this automatically. Later, we’ll discuss the different types of humidifiers and how each of them use their own unique method to improve the air quality in your home. For now, just remember that there are two general categories of humidifiers:

  • Whole-house humidifiers are connected to your existing HVAC system and your water line by an HVAC professional. They automatically control the humidity levels within your home.
  • Portable humidifiers are standalone systems with single room coverage that typically require you to manually operate them for humidity control.

What is relative humidity?

Now that you know what humidity is, let’s talk about relative humidity, which takes the concept one step further. The term humidity is actual moisture in the air, whereas relative humidity is the measure of how much moisture the air could potentially hold at a given temperature. This means, if the relative humidity is 50%, the air is only holding moisture at 50% of its capacity. If relative humidity is at 100%, the air is holding all the moisture it can, like during a rainy day in the summer.

The challenge is to maintain proper levels of humidity based on outdoor temperatures since the outdoor temperature directly affects the temperature of the air just inside your walls and windows, so it determines the amount of humidity you should add. The goal is to maintain comfortable levels of humidity without creating condensation on the inside of your windows. Generally speaking, the higher the indoor humidity during the winter, the more comfortable it feels (within recommended ranges.)

How to use a humidifier

While the exact instructions for how to use a humidifier depend on which model you have (more on that later!) there are a few universal tips and tricks to get the most out of your moisturizing system.

  • Choose a properly sized system for your home. Just like your HVAC systems, a humidifier needs to be properly sized for the space it’s working in. Consider the total cubic footage of your home, the age of your home, the construction (new, old, tight, reinsulated etc.) to determine the right sized system for your home.
  • Optimize your humidistat setting. When looking to invest in a humidifier, learn about the system and the settings available for you to use. Some humidifiers require you to manually control moisture levels while others can automatically do so. To use your humidifier to the best of its ability, select a model that meets your lifestyle needs.
  • Maintain your system. With frequent use, your humidifier will likely start to accumulate mineral build up, dust, rust, or bacteria. The best way to avoid any cleanliness issues with a portable humidifier is to regularly wipe down your system, flush the reservoir, and fill it with fresh water. You can do this with most simple household solutions and a rag, but it’s always a good idea to consult your humidifier’s owner’s manual for exact maintenance instructions. If you have a whole-house humidifier, maintenance is typically performed annually by your HVAC professional.
  • Select your optimal settings. When you invest in a humidifier, learn about the system and the settings available for you to use. Some humidifiers allow you to set up a schedule, while others give the homeowner the ability to control moisture levels. To use your humidifier to the best of its ability, make sure you customize it to your needs.

When to use a humidifier

Most households can benefit from using a humidifier, but there are a few signs to look out for that may indicate it’s time to invest in a system to optimize humidity and comfort in your home.

  • You get dry skin or chapped lips in your home.
  • You experience static shocks.
  • You’re frequently dealing with sinus issues or nosebleeds in your home.
  • You can’t sleep well throughout the night.
  • Your home’s interior is becoming damaged (chipped paint, cracking wood moldings around doors and windows, sagging or separated wood floors.)
  • You have consistent asthma or allergy flare-ups while inside your home.
  • You have to turn your thermostat up to feel comfortable.
  • Your plants are drying out.

If you face any of these issues, a humidifier could help alleviate some of the triggers.

Types of whole-house humidifiers

Whole-house humidifiers add humidity to the air and distribute that comforting moisture throughout your entire living space through ductwork. They’re installed directly on an existing HVAC system and are connected to your home’s water line.


Fan-powered humidifiers are a whole-home, evaporative humidifying solution. These types of humidifiers have their own fan to distribute moisturized air through the ductwork of your home so it works even when your furnace isn’t running. Fan-powered humidifiers have higher humidity output potential than bypass units making them an ideal choice for medium to large homes.


A bypass humidifier is the other main type of evaporative whole-home humidifier. It uses the HVAC system’s blower to push air through the unit and only operates when the furnace is running. Bypass humidifiers require extra ductwork, known as the bypass duct, and air must be recirculated back through the furnace before being distributed into the home. Bypass humidifiers have quiet operation, making them ideal for small to medium homes.

Whole-home steam

Some homes are very large and exceed the capacities delivered by evaporative whole-home humidifiers. In addition, some homes do not have forced air systems, but instead boiler (hot water) heat which means there’s no HVAC system blower or ductwork in the home. Finally, in some milder climates, a typical HVAC system may not run frequently, which would restrict the operation of an evaporative bypass or fan powered humidifier.

In these cases, a whole-home steam humidifier is the perfect solution. Steam is generated through a heating element inside a canister filled with water and uses your HVAC system to disperse that moisturized air throughout your home. For homes without ductwork, an optional fan pack can be used to distribute the moisturized air directly into the living space. These are high-capacity units which can deliver as much as twice the humidity as even the large fan-powered humidifier making them ideal for large homes and arid climates.

Types of portable humidifiers

Portable humidifiers are intended to change humidity levels in just one room or single space. These are standalone systems that you can place in the room of your choice, plus you can pick them up and move them around.


Evaporative portable humidifiers are one of the most common types of portable humidifiers. At the bottom of an evaporative humidifier, there’s something called a moist wick filter. To function, evaporative humidifiers use a fan that blows air through that moist wick filter, which then turns into a water vapor that is blown into the room to regulate humidity levels.

While evaporative portable humidifiers only work in one room, they’re a great option for people with children or pets because they don’t rely on heat to add moisture to the room. They’re also affordable and virtually noiseless.

Ultrasonic portables

Ultrasonic humidifiers use a reservoir of water and some kind of vibrating element, like a diaphragm. Inside the system, the diaphragm vibrates the water at an extremely high frequency. As these vibrations occur, water droplets are propelled into the air where they evaporate, to increase humidity.


Impeller humidifiers utilize a series of rotating disks that run at a fast speed inside the system to add moisture to the air, then redistribute it back into the room. Impeller humidifiers work well for people with changing humidity needs because the rotating disks inside can be set to different speeds and mist types,


The fourth kind of portable humidifier is the steam humidifier. The steam humidifier process starts when it senses a drop in humidity. Then, the steam humidifier begins to heat water in the reservoir of the system to turn it to steam and spray it into the air.

This means two things. One, a steam humidifier requires electricity to function, which many other humidifiers don’t need. Two, the steam distributed to add moisture into the air is hot, which could hurt if it’s sprayed directly on a person.

Which type should you use?

The type of humidifier you should purchase depends on your personal preferences and needs. Consider factors such as the amount of space you want to moisturize (size of your home), your budget, the level of maintenance you can tolerate, the furnishings in your home (wood floor warranties can be void if you can’t prove humidity control), and your family’s needs (children, pets, etc.) to determine the best humidifier for you.

Plus, if you’re choosing a whole-home humidifier, your HVAC contractor is the best resource as they will understand your HVAC system and can help you choose the model that best meets the needs of you and your family

Benefits of using a humidifier

As we’ve discussed, using a humidifier provides increased benefits to both your home and your health. After installing or purchasing a humidifier, some benefits you’re likely to start experiencing include:

  • Reduced heating costs.
  • Decreased health problems like sinus infections, asthma, and dry skin.
  • Fewer static shocks.
  • Better sleep and reduced snoring through the night.
  • Less structural and interior home problems like chipping paint, cracked molding around windows and doors, and separating wood floors.
  • Proper levels of humidity in all parts of the home.
  • Proper humidity with minimal maintenance.
  • Increased comfort and air quality within your home.

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