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How Does a Whole-House Humidifier Work?

Whole house humidifiers come in a variety of types: bypass, power and steam humidifiers all work slightly differently in providing your home with moisture to maintain humidity levels. What’s the difference, and which is the best type for you?

How Does a Whole-House Humidifier Work?

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Roger Bakies


December 24th, 2020

Dry, itchy skin. Cracked floorboards. Flu season hits harder than usual.

These are signs you need better humidity control in your home during the dry months of the year (usually the winter). And that means you need a whole-home humidifier.

Whole-house humidifiers are common add-ons to an HVAC system. They allow you to maintain a comfortable level of moisture in the air, especially during the colder, drier months.

But not all humidifiers are made the same. In fact, we’re going to discuss three distinct types of whole-house humidifiers in this article. They all work similarly, but some considerations may make one the best choice for your home.

We’re going to discuss each, and teach you about their inner workings. You may never have to know how to repair a humidifier, but understanding how each works can help to better explain why there are situations where one may be better than another.

QUICK NOTE: These are all ducted, whole-home humidifiers detailed below. While portable, single-room humidifiers can be good in a pinch, they don’t solve systemic problems with humidity in your home. They also won’t require professional installation, so there are fewer considerations when purchasing one.

Bypass Humidifiers

Bypass humidifiers use the airflow generated by your furnace - and more specifically, the blower fan in the air handler or furnace cabinet - to evaporate air.

A bypass humidifier sits on either the supply plenum or the return air drop area of your ductwork. Inside the humidifier, there is a panel. When there is a call for humidity from your system, the humidifier draws water and allows it to trickle down the panel.

The warm air from the furnace then blows over the panel, which causes the moisture droplets to evaporate. This evaporated air is then moved throughout your ductwork and home by the air supply coming from your system.

Bypass humidifiers get their name from the fact that they rely on the air from your system to pass through. As a result, it requires that your blower fan be on in order for the humidifier to do its job.

Power Humidifiers

Power humidifiers act similarly to bypass humidifiers, but they have their own fan inside of them. In this way, they facilitate the evaporation of air without needed air from the furnace or air handler to pass through.

Inside a power humidifier, you’ll find the same panel as you’d find inside a bypass humidifier, and water drips down this panel when there is a call for humidity.

The difference is that the internal fan in the power humidifier evaporates the water, and air channels on either side of the panel allow for a circular airflow within the unit. Once this evaporation takes place, the air travels through your ductwork system and into your home as usual.

For clarity, your air handler or furnace still needs to be running. The fan in the humidifier isn’t enough to get the moisture to travel through your entire home. But it does provide some extra power to facilitate airflow.

Home humidity control

Steam Humidifiers

Steam humidifiers have to boil water to create steam, as opposed to utilizing a fan or warm air from your furnace or air handler. There is a small pool of water in a steam humidifier, and this will be heated to produce steam that travels through your ductwork and into your home.

There’s no panel like you’d find in a bypass or power humidifier, but there’s an additional electrical component in a steam humidifier that allows it to heat the water into steam.

Pros, Cons and Comparisons

If they all do roughly the same thing, aren’t they all about the same? Well, sometimes.

For some homes, you could have any of the three types listed above and each would work well. Sometimes, however, there is a valuable benefit to one that won’t be available with another.

Size of Your Home

Humidifiers have different sizes and power levels depending on the square footage of your home. In the largest homes, you’d actually need more than one humidifier, since even the most powerful whole-home units have limits.

If you have a large home (3,000+ square feet), you’ll almost certainly need a Power Humidifier or a Steam Humidifier. Their methods of creating moisture and transporting it are better equipped for larger homes. If you have a smaller space to keep comfortable, a Bypass Humidifier is generally the best option.

Access to Hot Water

As you might suspect, warm or hot water evaporates more easily than cooler water. This means that the humidifier needs access to a water supply such as a hot water tank.

If this water isn’t warm, you’d be better off with a Bypass unit or a Steam unit, since these rely on other methods of heating the water. A Power unit will still produce humidity without hot water, but not at the same efficiency.

Maintenance Troubles

Technology has come a long way in recent years, so there isn’t a huge gap in reliability between the different types of humidifiers. However, historically, steam humidifiers have had issues with mineral buildup in their water supply.

You’ve probably seen or heard about this with portable humidifiers as well, many of which use similar steam technology. If you’re not careful with cleaning, mildew and mineral deposits can build up.

At Fire & Ice, we install Aprilaire humidity products. We like this brand, because they’ve found ways to reduce these deposits to the point where regular yearly maintenance (which you should be getting done anyway for your HVAC system) is enough to handle any potential problems.

However, this wasn’t always the case, and we can’t speak for every brand on the market. Aprilaire is a large national supplier, but others exist throughout the country.

Humidifier Maintenance, Operation & Installation

Let’s run through some FAQs and considerations for whole-house humidifier installation and maintenance:


  1. Do they need maintenance? Yes, this should be done on a yearly basis, just like any piece of HVAC equipment.
  2. Does humidifier maintenance cost money? Yes, but it can generally be rolled into the cost of a full system tune-up for your furnace, heat pump, or air conditioner.


  1. Can a humidifier be installed at any time? Yes, it doesn’t have to be when you install new ductwork or a new furnace or air conditioner. In fact, we often have people call us after a new installation to add in a humidifier.
  2. Is there ever a time when a whole-home humidifier can’t be installed? Yes. You need to have room for it to fit, so a furnace or air handler in a tight closet might not have enough room. You also need to have access to a water supply and a floor drain. Running a drain line outside would risk freezing over in the winter. The same is true of the humidifier itself, which can freeze if it’s in an unconditioned space (such as an attic).


  1. Does the humidifier have to run year-round? No. You can usually set it to come on only when your system is heating. Many bypass humidifiers also come with manual dampeners so that you can manually close it off from your system if your home is humid enough.
  2. Can I control the humidity from my thermostat? It depends on the thermostat and the wiring you have running to it in your home. Many times, the answer is yes. But even when you can’t, a control panel on the ductwork near the humidifier will let you control it as well.
  3. Can humidifiers adjust on the fly to my house? Yes, you’ll often be able to set a humidity level and the humidifier will work until it reaches that level. Some sophisticated models have outdoor sensors as well, to adjust naturally with outdoor temperature (since high humidity in cold climates can produce window condensation).
  4. How much energy and water does the humidifier use? Relative to your regular water bill, you shouldn’t see a huge spike in utility costs except in the driest climates. The electrical burden is also very little. Steam humidifiers use more than the other two types, but shouldn’t make a large dent in your overall electrical bill. The other two types use even less, and outside of a small solenoid valve in a bypass humidifier, that style of humidifier uses almost no electricity.

Moisture on a window

Price of a Whole-Home Humidifier

The price of a whole-house humidifier, including installation labor costs, can range from $600 to $2,500.

Does that seem like a wide range? The biggest difference is home size. The style of humidifier makes a difference as well (power humidifiers start at about $800, for example).

Want the full rundown of cost considerations, to get you closer to an expected total? Check out our article below on humidifier cost!

ALSO READ: Is a Whole-Home Humidifier Right For Me? Full Cost Analysis Included

The cost is a drop in the bucket (or drop down the evaporator panel) compared to the long-term benefits of a whole-home humidifier. They can even lower your winter utility bills!

If you live in an area with dry winters and plan to spend more than five years in your current home, we absolutely recommend a whole-house humidifier.

And if you’re in Columbus, OH, we’d be excited to be your installer. Give us a call or enter your zip code below to start the process. And before you go, check out these awesome resources to learn even more about how to keep your home comfortable year-round!


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