How Does A Whole House Humidifier Work? (2024 Guide)

Do you want to know how a whole house humidifier works?

In essence, these humidifiers work by sending water vapor into the HVAC ductwork, but there are also portable units that can do it without ducts.

In this guide, I will go over...

  • How steam whole house humidifiers work
  • How evaporative whole house humidifiers work
  • And how console whole house humidifiers work

Let's get started with this guide!

how does a whole house humidifier work

The Basics Of Whole House Humidifiers

Whole house humidifiers work by putting moisture into the air in order to raise the indoor relative humidity.

When a home's indoor humidity level drops below the desired or set level, the humidistat (controller) sends liquid water to the evaporator panel (or canister for steam). And the liquid water turns into water vapor which is sent throughout the entire home.

Ideally, homeowners want at least 30-50% relative humidity for the most comfortable home. Many people don't realize that the humidity of a home can have such a high impact on comfort. It is even possible to lower the HVAC thermostat because moistened air retains more heat.

Whole house humidifiers, either through steam or vapor, increase the home's moisture. There are a few main types of whole house humidifiers, steam, bypass (and fan powered), as well as console units.

Read Also: What Are The Best Whole House Humidifiers?

1. Steam Whole House Humidifiers

Steam whole house humidifiers produce moisture in the form of steam rather than water vapor. These HVAC humidifiers rapidly boil liquid water which turns into steam. Since the humidifier is built into the HVAC ductwork, the steam can be sent throughout the entire home.


These central humidifiers use two electrodes that are submerged in water.

When the humidity of the home drops below the set level, the humidistat of the steam humidifier sends an electrical current to the two electrodes. And since water already has a natural conductivity because of its mineral content, the electrical current quickly boils the surrounding water which results in high quality steam.

Filled From Bottom

Another difference between steam whole house humidification systems and the evaporative type is that steam humidifiers are filled with water from the bottom. Evaporative whole house humidifiers have their panels filled with water from the top.

And similar to evaporative whole house humidifiers, steam units have drain valves and drain piping at the bottom of the humidifier which will drain away unused water.

These steam humidifiers have controllers that will adjust the water level to maintain the correct conductivity of the water, and to produce the right amount of steam.

Once the water starts boiling, the resulting steam is sent into the ductwork through something called a 'dispersion tube'. The dispersion tube sends the steam into the ductwork in as wide an area as possible, and it also acts to drain any condensed water back into the tubing rather than in the ductwork.

Read Also: What Are The Pros And Cons Of Whole House Humidifiers?

steam vs evaporative whole house humidifier (digital control)

2. Evaporative Whole House Humidifier

Evaporative whole house humidifiers work very similarly to steam humidifiers, except that they use natural evaporation rather than steam. These humidifiers typically send around 10-20 gallons of water into the air as water vapor.

Evaporator Panels

In essence, these humidifiers pour water over an evaporative panel (also called a pad), and as this panel is soaked in water, air is blown over the panel which causes natural evaporation. And this water vapor gets sucked or pushed into the HVAC ductwork and then throughout the entire home.

With most evaporative whole house humidifiers, they only turn on when the furnace or heat pump is actually running, and the blower fan is on. With some units, they can be wired to turn on the HVAC system itself when moisture is needed in the home, but a hot water supply is usually needed (as well as the cold).

Basically, when the humidistat (which detects indoor relative humidity) detects a drop in home moisture, below the set level, the humidistat or controller sends a signal to the water valve.

The water valve opens and sends water to the distribution tray which sits above the evaporator panel or pad. The distribution tray even spreads the water, and then gravity naturally pulls the water down into the panel which soaks it.

Evaporative humidifiers have drains on the bottom which diverts the unused water to a nearby floor drain or to the exterior. To verify that the humidifier is actually operating, all you have to do is inspect the drain hose (usually clear tubing) to see if there is a small stream of water.

Read Also: What Are The Best Steam Whole House Humidifiers?

Fan Powered Whole House Humidifiers

Probably the most common type of evaporative whole house humidifier is the powered unit. These whole house humidifiers have their own power supply and fan.

This means that a separate bypass duct is not required, and the whole house humidifier uses its own fan (rather than the HVAC blower fan) to distribute water vapor into the ductwork.

The nice thing about these powered humidifiers is that the installation is easier since there is no extra duct needed. They also tend to need less maintenance than bypass humidifiers.

The evaporator panels or pads need to be changed annually with these humidifiers, and with some models may need to be changed twice a year.

Bypass Whole House Humidifiers

The second most common type of evaporative whole house humidifiers is the bypass type. These humidifiers have a small section of duct that connects the HVAC system to itself.

When the HVAC system is on, the humidifier diverts some of the dry air flow into the humidifier, which goes through the evaporator panel. This humidified air gets sucked back into the HVAC ductwork and then throughout the entire home.

Read Also: What's The Difference Between Steam And Evaporative Whole House Humidifiers?

3. Console Whole House Humidifiers

Console whole house humidifiers are portable units that are rated for entire homes or large areas. 

These humidifiers are much higher capacity and stronger than the smaller table top humidifiers that are common for bedrooms. These hefty humidifiers typically hold anywhere from 3 to 6 gallons of water and can do a great job for smaller homes or single levels.

If you want to see my top picks of the best console whole house humidifiers, you can read it here.

The nice thing about console whole house humidifiers is that there isn't a complicated or costly installation such as HVAC humidifiers. These humidifiers can be a setup in a few minutes and sending moisture into the air.

They work on the same principle of evaporation as HVAC evaporative whole house humidifiers. Basically, when the humidity level drops below the set level, water is then sent above a 'wick' which becomes saturated in water. Air is sucked in through a vent at the back of the humidifier, which goes over the wick, and then the humidified air is sent into the room.


Unfortunately, these console units simply will not work as well as HVAC humidifiers, and you may have trouble reaching the desired moisture level throughout the entire home. One way to get a better distribution of humidity with these portable units is to place the humidifier near a return HVAC vent.

Also, these console whole house humidifiers have to be frequently filled back up with water or they will stop working. Most console units will have to be filled anywhere from 1-3 days if they are being consistently used.

The wicks will also have to be replaced every 30-60 days if they are used often. If you use purified or distilled water rather than tap water, the wick may last much longer due to less mineral buildup (white residue) on the wick.

I also recommend that homeowners keep on eye on the cleanliness of these humidifiers because mold or mildew growth is a possibility. There are bacteriostat treatments made for humidifiers that can be poured (some tablet form) into the humidifier which will prevent mold growth.

Read Also: Whole House Humidifiers And Mold

Final Thoughts

At its most basic level, whole house humidifiers use a humidistat to sense the moisture in the air. And when the humidity drops below a set level, the humidifier turns on and sends water to a wick or evaporator panel. Air then blows over this saturated panel and the newly humidified air gets sent throughout the entire home.

Steam whole house humidifiers are very similar except that they boil the water to create steam.

Console whole house humidifiers are the only type that aren't connected to the HVAC ductwork. They are cheaper than HVAC mounted humidifiers, but they are not as effective.

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