Humidifier

What is a Humidifier and Do You Need One?

By Anne Fonda

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

Signs of low indoor humidity 

When humidity levels are lower than 30%, you might be met with physical issues like dry skin, static shocks, or sinus infections. In your home, you may notice cracking wood or chipped paint.  

A humidifier works to reduce these problems by raising the humidity level in your home to keep it within that optimal range, and the best ones do this automatically. There are two general categories of humidifiers: 

• Whole-house units can operate independently or in tandem with your HVAC system and connect to your home’s water supply. An HVAC professional should install it. They automatically control the humidity levels within your home.  

• Portable units are standalone systems with single-room coverage that typically require you to manually operate them for humidity control. You must also refill the water tank with water or distilled water and clean them regularly. 

How does a humidifier work? 

During the cold winter months (or year-round in a dry climate), you might notice a drop in humidity. With whole-house humidifiers, you can set the desired humidity level on your programmable or smart thermostat. Humidity sensors trigger the unit to start adding moisture to dry air, using water from the water supply line. The unit shuts off when the desired humidity level is reached. 

With portable humidifiers, you set the desired humidity level, and they run until you turn them off or the water level is too low for safe operation. Some more advanced models have a timed shutdown capability, while others with built-in humidistats shut down once they reach the set humidity level. They can start back up when humidity levels drop again.  

How to use a humidifier 

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

• 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 (or room for a portable unit), 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, a portable humidifier may accumulate mineral buildup, mold growth, dust, rust, or bacteria. The best way to avoid any cleanliness issues with a portable unit is to empty the reservoir daily, clean it with a 50/50 solution of white vinegar and water weekly, and fill it with fresh distilled water. If it has a wick or filter, refer to your owner’s manual for exact maintenance instructions.  

For many whole-home systems, maintenance is simple. Just replace the humidifier pad yearly, and follow the instructions in your owner’s manual. For some systems, you may need an HVAC professional to perform a yearly checkup. 

• Select your optimal settings. Some humidifiers allow you to set up a schedule, while others give the homeowner the ability to control moisture levels. To use your system to the best of its ability, make sure you customize it to your needs. 

When to use a humidifier 

Whether the air is dry in the winter or you live in an arid climate, watch out for these signs that indicate you have low humidity in your home.  

• You get dry skin or chapped lips in your home. 
• You experience shocks from static electricity. 
• 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 warm enough in the winter. 
• Your plants are drying out. 

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

Benefits of using a whole-house humidifier 

After installing a whole-home 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 indoor air quality. 

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 

Fan-powered humidifiers are a whole-home, evaporative humidifying solution. These units 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. 

Bypass 

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 

A whole-home steam humidifier is the perfect solution for homes up to 5,000 sq. ft. It offers humidity on demand, whether your HVAC system is running or not. It generates steam by using a heating element inside a canister filled with water and sends it through your ductwork 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.  

Types of portable humidifiers 

Portable humidifiers are intended to change humidity levels in just one room or a single space. These are standalone systems that you can place in the room of your choice. Using distilled water is recommended. 

Evaporative 

Evaporative portable humidifiers are one of the most common types of portable units. They’re commonly known as cool mist 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 the moist wick filter, which then turns into water vapor that is blown into the room to regulate humidity levels. 

Ultrasonic portables 

Ultrasonic humidifiers are also cool-mist humidifiers. They 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, increasing humidity. 

Impeller 

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. 

Steam 

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, because they heat water, they could cause a burn if they tip over or the mist blows directly on someone.  

Which type of humidifier 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 humidify (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. 

Portable units are a great temporary solution and require weekly (if not daily) maintenance. This includes filling the water reservoir and cleaning the inside of the unit. Whole-house humidifiers are a permanent solution for homes in areas with dry winters or homes in dry climates. Plus, they don’t require much maintenance on your part – no filling a reservoir or cleaning the unit weekly.  

If you’re choosing a whole-house humidifier, work with your HVAC contractor to help you choose the appropriate model.  

Why you can trust us 

When we compile information like this, our goal is to help homeowners make informed decisions. We work with HVAC engineers and HVAC professionals with decades of experience. We provide you with accurate and up-to-date information. Our glossary items and blogs undergo expert review to ensure you get the information you need. 

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Anne Fonda, Content Writer

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A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.

When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Jennie Bergman, Senior Product Manager, Indoor Air Quality