How Does a Whole-House Humidifier Work? (Explained!)

Are you always coughing in your home? Are your wood floors cracking? Are your nose and throat always uncomfortably itchy?

I once answered “yes” to all these problems. Fortunately, getting a whole-house humidifier helped resolve them — and it can do the same for you!

Whole-home humidifier units can be expensive, though. You should know how they work so you can invest in the right kind of machine.

I wrote this guide to help you understand how the most popular whole-home humidifiers work, so read on!

How Does A Whole-House Humidifier Work?

Whole-home humidifiers are stationary devices that connect to your home’s HVAC system and ducts to add moisture to dry indoor air.

My unit has really boosted the humidity levels in my home and improved my indoor air quality. I now have much fewer breathing issues, thanks to the device.

Each type of humidifier must be connected to a water supply line, as they need water to produce moisture. How they turn water into vapor or mist and move it into your home depends on the device.

Here are my explanations of the four main types of whole-house humidifiers:

Steam Humidifiers

Steam humidifiers are among the most precisely controlled methods to increase moisture levels in your home. They boil water to create steam, which boosts humidity in your home.

The steam humidifier draws water into an internal reservoir, which is attached to or surrounded by an electrical heating system. The humidifier heats the water to the boiling point, producing steam. It then releases the steam to your heating ducts to spread it throughout the house.

Steam humidifiers are very efficient at boosting humidity levels and I can heartily recommend them for large homes. However, boiling the water consumes power and it may raise your energy bills noticeably.

Steam Humidifier

Bypass/Flow-Through Humidifiers

Bypass humidifiers, also called flow-through humidifiers, are very simple furnace humidifiers. A bypass humidifier consists of a water connection and a water-absorbent material called a moisture or humidifier pad.

The device is installed into an air duct connected to your HVAC system. As it’s turned on, the water line soaks the moisture pad with water. The air flow from the furnace passes by the pad (that’s where the name comes from!) and evaporates the water, pushing the water vapor into your home.

Unlike a steam humidifier, a bypass humidifier doesn’t use any electricity, which I really appreciate. It can be a very affordable and low-maintenance humidifier option, particularly for small homes like mine. However, you do need to install a collection tray and a drain line to prevent water damage from potential leaks.

Flow-Through Or Moisture Pad Humidifiers

Drum Humidifiers

Drum humidifiers are a variant of flow-through humidifiers. They also feature a water connection and an absorbent moisture pad. However, the moisture pad is housed in a rotating drum.

The drum sits above a shallow water pan with an automatic fan to maintain an appropriate moisture level. As the drum rotates, it dips the pad into the water, absorbing moisture. Warm air flows from your furnace into the middle of the drum and through the soaked pad, drawing moisture into the indoor air.

Drum humidifiers can be very affordable and efficient, and won’t consume as much electricity as steam units. However, they need regular maintenance to prevent mold growth in the drum and moisture pad. As such, I wouldn’t recommend them if you suffer from allergies or asthma like I do.

Drum Humidifier

Power Humidifiers

Power, or fan humidifiers, function similarly to bypass and flow-through humidifiers. But in addition to the basic bypass unit’s components, they feature an independent blower fan that pushes air through the moisture pad.

The greatest advantage of power humidifiers is that they can work even when you’re not running the furnace. They consume some electricity, but in exchange, they can humidify your home year-round, even when you’ve turned the heating system off.

Power humidifiers can be really awesome if you live in a dry and hot area, like a desert.

Major Components Of Whole-House Humidifiers

In addition to knowing the basic operational principles of whole-house humidifiers, it’s good to be familiar with their main components. This way you can communicate better with your HVAC technician — or even do DIY maintenance.

Here’s my breakthrough of a basic whole-home humidifier’s parts (just note that they may differ between units):

Water Tap/Supply Line

The water supply line connects your furnace humidifier to the local water service. The line allows the machine to draw in water that it transforms into air humidity.

Water Inlet Orifice

The inlet orifice controls the water flow into the humidifier. It prevents too much water from entering the device and potentially flooding it.

Water Inlet Valve

The inlet valve, located after the orifice, allows water to flow into the humidifier based on demand. Generally, the inlet is an electrical solenoid valve connected to a humidistat.


The humidistat is located outside the humidifier, where it monitors air humidity and provides humidity control by turning the machine on or off. I like to think of it as a thermostat, except that it reads the humidity level instead of the temperature.

Water Feed Tube

The water feed tube or tubes are responsible for circulating water internally through the humidifier. They transport water from the inlet valve into the evaporator pad or the tank.

Water collector

In most whole-home humidifiers, the water collector is an evaporator pad that soaks up water for evaporation. In a steam humidifier, however, a water tank takes the pad’s place.

Evaporator Pad

Drain Pan

The drain pan sits under the evaporator pad to catch any leaking or spilled water. It has a drain line that empties the pan into your home’s drainage system. It’s important to keep that drain line clean — I can tell you that an overflowing humidifier is not a pleasant surprise.

Air Damper/Air Duct

Some humidifiers integrate with an air conditioner to humidify both warm and cool air. These units require air ducts and dampers. The configuration allows the system to feed either hot or cold air to the humidifier without affecting its temperature.

When Do you need a whole-home humidifier?

Most people purchase a portable humidifier to treat dry air in a certain space, like a bedroom. However, you should consider purchasing a whole-home humidifier if you notice symptoms caused by dry air throughout your home.

I live with breathing issues and am all too familiar with the most common dry air symptoms. Keep an eye out for problems such as:

  • Persistent coughing, runny nose, nosebleeds, or stuffy throat
  • Sinus issues or asthma attacks
  • Dry or itchy skin or other skin conditions
  • Regular colds or flu that last a long time
  • Dry and cracked wood furniture

Benefits of Humidifying Your Entire Home

Humidifying your whole home isn’t difficult and gives you a range of benefits that you’ll start to feel almost immediately. Here are my top reasons to install a whole-home humidifier:

Improves Your Health

Humidifying your home improves the overall air quality. This helps reduce the risk of airborne diseases or infections like coughs and colds. It can also help regulate air pollutants that can cause respiratory irritation and asthma symptoms — which is a big personal plus for me. (1)

Increases Comfort

Dry air can irritate your skin and your respiratory system, making you itchy, giving you a sore throat, and drying out your skin. It can also increase the levels of airborne allergens. Air humidity in the 30-50% range throughout your home can help relieve these issues.

Preserves Your Home

Dry air can damage your home. Your floors can crack, wallpaper peel, and paint can begin to chip. Your wood furniture may experience dry rot, and excessive static electricity could harm electronic appliances.

A good humidifier will help protect your home from unnecessary damage. I like wooden furniture, so the added humidity has been a welcome addition.

Saves You Energy & Money

You can actually save a great deal of money with a whole-house humidifier. Maintaining an appropriate humidity level makes you feel warmer and allows you to save money and energy on heating during cold winter months. Additionally, by protecting your home’s surfaces, you may avoid costly renovations.

How much do Whole-House Humidifiers Cost?

I can’t tell you exactly how much whole-house humidifiers cost, since they are available in a wide price range. The cheapest units can cost just a couple hundred dollars, while big high-end devices could cost several thousand dollars.

The price of the humidifier unit depends on its type and size, the size of your home, and your air conditioning system. You will also have to pay for the energy and water the device consumes, in addition to humidifier maintenance, such as filter replacements.

You might also want to hire a professional to install the system. It’s possible to save some costs by handling humidifier installation yourself, but I recommend turning to a professional to avoid damaging your HVAC system.

Whatever you end up paying, though, the health benefits will likely outweigh the price!

How To Install A Whole House Humidifier (6-Step DIY)

Installing a whole-house humidifier can be simple if you’re good at DIY projects. First, you need the right equipment. You’ll need:

Once you’ve got everything ready, follow these steps:

1. Cut The Humidifier Outlet Hole: Mark the outlet hole’s position on the air supply duct. The manufacturer will typically provide a template and instructions on how to do this. Use the drill and aviation snips to cut the section out and attach the mounting plate with screws.

2. Cut The Humidistat Hole: Following a similar process, mark and cut a hole for the humidistat. Refer to the manufacturer’s guidelines for the size and positioning of the hole.

3. Install The Humidistat: Mount the humidistat and screw it in place. Follow the instructions and connect the furnace controls to the humidistat.

4. Wire The Humidifier: Switch off electricity in your home and connect the wires from the humidistat to the humidifier. The humidistat should connect to the humidifier’s solenoid valve.

Humidifier Thermostatic Wiring Diagram

5. Connect The Water Line: Install a saddle valve into your water line and connect it to your humidifier. Fasten it with a compression fitting.

6. Run The Humidifier: With all the connections in place, your humidifier should work. Turn the power back on and test the unit.

Note that you will have to deal with potentially dangerous electrical and water lines. If you’re not 110% certain about what you’re doing, I recommend hiring an HVAC professional to install your humidifier.

It will be cheaper than fixing electrical or water damage!

A full guide to installing a whole-house humidifier can be found here: How to Install a Whole-House Humidifier | Ask This Old House – YouTube

People Also Ask (FAQ)

How do I know if my whole-house humidifier is working?

You know your furnace humidifier works if you can see and hear it power on and can see water running through the system. If you don’t hear or see this and the air in your home stays dry, call an HVAC professional.

How long does a whole-house humidifier take to work?

A whole-home humidifier typically takes around 24 hours to humidify the whole house. The exact time will depend on the type of humidifier and the size of your home.

Do whole-house humidifiers cause mold?

A whole-house humidifier could cause mold if you allow it to over-humidify your home. Ensure the system has a functioning humidistat and change the humidifier filter regularly to prevent mold.

Are whole-house humidifiers dangerous?

No, whole-house humidifiers aren’t dangerous when operated correctly. That said, excessive humidity could cause mold growth and health issues. Make sure you have a way to monitor humidity levels in your home with a hygrometer or humidistat.

How long do whole-house humidifiers last?

With proper maintenance, a whole-house humidifier can last 10-15 years, depending on the type and brand. Take care of your system and you can enjoy it for years to come.

Where should I put my whole-house humidifier?

Furnace humidifiers are always located on your furnace or heat pump, or the HVAC system near it. Portable “whole-house” humidifiers, meanwhile, should be placed at a central location in the busiest room of the home for maximum benefits.

Are whole-house humidifiers loud?

Whole-house humidifiers should not be loud. They’re relatively quiet and usually located where you can’t hear them. If your humidifier is noisy, it likely has a problem and requires maintenance.


If you’re like me and live with breathing issues in a very dry location, a whole-humidifier can be your key to easier breathing. You just have to find a unit that’s suitable for your home’s size and climate.

Armed with my guide and tips, you can choose a humidifier that’s ideal for your home. With the right machine, you’ll soon enjoy increased comfort and healthier air quality in your home.



Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.