Steam Vs Evaporative Whole House Humidifier (2024 Guide)

Are you interested in learning the differences between steam and evaporative whole house humidifiers?

These are the two main types of central home humidifiers, and they both have their pros and cons. Which is right for you? 

In this humidifier guide, you will learn...

  • The main differences between steam and evaporative humidifiers
  • Pros and cons of each type
  • Learn about the sub-types of evaporative whole home humidifiers
  • Which works better?

Let's get started with this guide!

steam vs evaporative whole house humidifier

What Is A Steam Whole House Humidifier?

A steam whole house humidifier is a humidifier that produces steam (a form of water vapor) by boiling water.

The main purpose of whole house humidifiers is to maintain the humidity of a home at a comfortable level (or to ease the symptoms of an illness).

Electrode Technology

The steam humidifier uses two electrodes submerged in water. The electricity produced by the electrodes heats up the water, and the water then releases steam.

The steam is released into the ductwork, and the air handler's blower fan pushes this steam around the home during normal heating. With a steam humidifier, it can operate with or without the heat actually being on --- but it does turn on the blower fan at a minimum.

In general, if you have ductwork in unconditioned space, such as in an unfinished attic, you probably only want to use the humidifier when the heat is on so that condensation doesn't form on cold air ducts and possibly lead to mold problems.

Read Also: The Best Steam Whole House Humidifiers (Which Are The Best?)

Cool Mist Humidifiers

There are also free standing whole house humidifiers that produce cool mist, but this isn't technically considered steam since water isn't heated or boiled. Also, these humidifiers are usually just for large rooms and not suitable for a whole house.

What Is An Evaporative Whole House Humidifier?

An evaporative whole house humidifier uses evaporation to release humidity into the home's air. Evaporation is the process by which liquid water turns into water vapor. (Approximately 90% of the earth's water is released back into the atmosphere through evaporation.)

Basically, the evaporative whole house humidifier pours cool liquid water over a evaporator panel (looks like a big filter), and then air is blown over the pad. The water evaporates and vapor is sent into the HVAC ductwork --- thereby raising indoor relative humidity.

Read Also: The Best Whole House Humidifiers (Mostly Evaporative)

dirty evaporator panel

Once the humidistat (humidity sensor) detects that the indoor humidity has reached it's set humidity level, the humidifier will stop.

There are three main types of evaporative whole house humidifiers...

#1. Portable Whole Home Humidifier

The portable type of whole house humidifier is a free-standing humidifier that isn't connected to ductwork. These units are generally rated for smaller homes up to around 2400 square feet. 

I'm sure you have seen one of these smaller humidifiers before, they are extremely widespread and popular. About 96% of the humidifier market is for these portable humidifiers.

Similar to HVAC connected humidifiers, the console type also uses evaporation to send moisture into the home. It does this by using a media suspended in liquid water with air blown over it. Likewise, the console types have humidistats that will detect the indoor relative humidity so that you know when to turn it off.

Unfortunately, with console humidifiers, you will have to repeatedly fill the humidifier with liquid water for it to keep running. Some humidifiers have larger water tanks than others.

The EPA also recommends cleaning these portable humidifiers every three days.

#2. Bypass Humidifier

The bypass humidifier is the older and traditional HVAC connected whole house humidifier.

It uses a bypass duct that connects to the return side of the HVAC system. Water pours over a "pad" called the evaporator panel, and when the heat is on, the heated air "bypasses" the furnace or heat pump and blows over the evaporator panel --- thereby sending excess moisture into the air duct system.

In essence, the bypass whole house humidifier is unpowered --- there is no fan. It uses the blower fan of the furnace (or air handler) as well as the heated air.

bypass whole house humidifier

#3. Powered

The powered evaporative whole house humidifier is similar to the bypass except that it has a powered fan so it doesn't need a bypass duct. This type of humidifier is installed on the supply side of the air handler and it directly blows the humidity into the air ducts when the heat is on.

During my home inspections, this is the most common type of humidifier that I see installed on newer homes.

powered whole house humidifier

Read Also: The Best Programmable Thermostats Under $50

What Is Better? (Steam Or Evaporative?)

The Best Of The Best Is Steam

In my opinion, the best whole house humidifier is definitely the steam humidifier. The steam whole house humidifier is just much more efficient, more accurate, and produces more steam.

The average evaporative humidifier can take up to 14 gallons of water to produce just one gallon of water vapor.

With a steam humidifier, it is more like 1 to 1, one gallon of water produces one gallon of steam.

The maintenance is also much simpler because you just have to replace the console annually (where the electrodes are located) and you don't have to do any cleaning.

The steam also tends to be a higher quality water vapor than ordinary evaporative humidifiers.

steam vs evaporative whole house humidifier (digital control)

Powered Over Bypass Any Day

In regards to bypass versus powered, in my opinion, powered it better than bypass for a number of reasons.

In my experience, the interior air handler or furnace is a common place for mold to grow. This is because it has the three things that mold loves --- darkness, moisture, and dust.

And then with a bypass humidifier, it adds even more moisture to the air handler because it is installed on return side of furnace.

steam vs evaporative whole house humidifier

Read Also: The Best UV Lights For HVAC (Prevent Mold)

With a powered humidifier, it it is installed on the supply side so the moisture doesn't have to go through the actual air handler, it goes directly into the ducts.

Also, bypass humidifiers don't work so well with heat pumps because the air isn't as hot as would be with a gas-fired furnace. But with a powered humidifier this doesn't matter.

And Last Place Are The Portable Whole Home Humidifiers

Even though portable whole home humidifiers are advertised as for a whole house, they are usually rated for up to around 2400 square feet. Larger homes just don't stand a chance with these free standing humidifiers.

But even on a normal sized house, the portable whole home humidifier probably won't be enough, you may need to have two or three to do the job.

There are number of things to consider, but for one, at least where I live --- most of bedroom doors are left closed --- so this would restrict moisture from reach those areas. These humidifiers don't have the coverage compared to the HVAC connected humidifiers.

It's hard to compete with ductwork that goes throughout the entire home. 

But, these portable whole home humidifiers are definitely cheaper when you factor in installation costs.

If you have a small home, or just want it for a particular area, then give it a shot, they can be fairly inexpensive and there is no extensive installation like with HVAC humidifiers. Just remember that you will have to keep refilling the water tank and clean it to prevent mold!

Read Also: My 6 Pros & Cons of Whole House Humidifiers (Detailed Guide)


In my opinion, steam whole home humidifiers are the absolute best humidifiers on the market --- but they are also the most expensive.

These steam humidifiers just produce better quality humidity.

For one, you are more likely to reach your desired humidity level with a steam whole home humidifier.

They also just so much less water --- usually one gallon of water for one gallon of steam.

There is also much less maintenance. I can't even tell you how many home inspections I have performed where the evaporative whole home humidifier had a disgusting pad that probably hasn't been changed in years.

It is never a good thing for a buyer to see a dirty whole home humidifier... they may start wondering what else you haven't maintained.

With steam whole home humidifiers, there is no pad to replace. With the Aprilaire 800, you just replace the console once a year. The console is the removable part that contains the electrodes that heat the water for steam.

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6 thoughts on “Steam Vs Evaporative Whole House Humidifier (2024 Guide)”

  1. What does it mean to take 14 gallons of water to produce 1 gallon of vapor. where is the other 13 gallons going !

    • Haha! With evaporative humidifiers, water is drips down a pad/filter which then drains out of a clear tube on the bottom. Most of the h20 stays liquid and the humidification is indirect with air blowing over the pad. With steam units, it is converted more directly into steam/vapor.

  2. I appreciate your article: Steam Vs Evaporative Whole House Humidifier (2021 Guide). I have a whole home steam humidifier and the Aprilaire 800. It keeps humidity fairly constant in our home. I had it installed with new AS HVAC equipment in 2020. You say it is more effecient for water usage which I would agree, but electricity is a completely different matter. I eatimate on typical winter days it consumes 10-30 KWh depending on outside temps and humidity which adds up. Fortunately in KC, the electric utility charges less for electricity than in the summer. My consumption was only a few hundred off my summer AC. That tells me that steam unit chews as much or more electricity than a full size electric hot water heater. My home has leaky exterior doors which allows a lot of unconditioned air in which I’m in the process of replacing. I’m hoping my HVAC and humidifier cost will go down as a consequence.

    Great article, but would be good to inform those that consider steam humidification of the high electricity usage to help them make an educated decision

    I had a Aprilaire powered evaporative humidifier before that in another home that was similarly sized and it was able to keep up, but did take longer to do so. It was much more cost effective to run.

    Have a great day!


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