What are Furnace Humidifiers?

Adam Hill
Adam Hill
An ideal humidity level is about 45 percent.
An ideal humidity level is about 45 percent.

Furnace humidifiers are the best way to control the relative humidity of all the air in a house. They are installed as part of the ventilation ductwork near a furnace, and provide humidity whenever a furnace is running. Generally speaking, furnace humidifiers are fitted when a heating system is installed, since they are designed to be fully integrated into it.

All furnace humidifiers apply the same basic principles to humidify hot air, but they come in two basic types. The first type is a flow-through design, where water flows into a humidifier and then drains out. These are commonly mounted on the air return duct on the furnace and connected to its hot air supply. Inside the humidifier, warm air absorbs moisture from an evaporator pad, and from there goes into the furnace to be dispersed throughout the house.

Furnace humidifiers also come in a second variety, namely the reservoir humidifier. In this type, there is a reservoir of water and a rotating drum to introduce moisture into the air. One risk associated with these humidifiers is that in some cases, bacteria and mold can grow in the reservoir’s standing water. Microorganisms like these can lead to humidifier fever, an inflammation of the lungs. However, proper care and cleaning of the reservoir can reduce or eliminate this risk.

Airborne pollutants were a common problem associated with earlier designs of furnace humidifiers which used an evaporative wick. In these types, a sponge was used to soak up water which was then passed into the air. Not unlike the way a dish sponge can grow mildew over time if not kept dry, these sponges easily became breeding grounds for such organisms. Frequent cleaning or replacement of the sponges was the only way to avoid contamination of the air inside a home.

Thankfully, today’s designs are much safer and require less maintenance. Another convenient feature that comes with some newer furnace humidifiers is a humidistat. In the same sense that a thermostat regulates temperature, a humidistat regulates the relative humidity of a home. These units measure the moisture content of the air coming into the humidifier and adjust its function accordingly.

While furnace humidifiers are convenient, some prefer tabletop humidifiers that serve only a single room. These do have advantages over whole-house humidifiers since they are uncomplicated and do not need to be installed by a professional. The smaller, more portable humidifier may be the preferred alternative if only one room needs extra humidity.

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Discussion Comments


Is the wheel with the sponge that spins in the water suppose to turn all the time the blower is running on my furnace?


We are buying a home with a new furnace with built in humidifier. Do not know the brand, etc., but am glad found this site, and we will get all the paperwork on the furnace.

Both hubby and I have had coughs for over a month. We are renting a house. I hope when we get to our new place, the humidifier helps a little.


For years my parents had a reservoir humidifier in their home. My dad ended up getting sick about the same time every year, and for a long time they couldn't figure out what was causing it.

They finally figured out it was from the mold and bacteria that was growing in the water reservoir from the humidifier. Something they thought was helping them out was actually causing them harm.

Since then they have switched to a unit that connects to their air return duct. They didn't want to continue taking any chances and this one requires less maintenance.


The two rooms I spend the most time in are the bedroom and my office. I don't have to worry about the lack of humidity in the summer, but the winter can be tough.

I ordered some portable humidifiers that are supposed to work similar to a furnace steam humidifier.

These are plastic grids with sponges that sit on top of the furnace vents on the floor. You fill these sponges with water and as the heat comes through your vents, the moisture is spread throughout the room.

I can add essential oils to these so in the bedroom I can add some drops of lavender to help me sleep. In my office I use peppermint to help keep me alert.

I can smell the aroma from the oils, so know they are working. While something like this wouldn't be as effective as a whole house unit, it helps a little bit and didn't cost much money.


@starrynight - That is good to know your parents have had good results with a humidistat.

The air in our house gets so dry in the winter time. If we don't keep humidity in the air, my husband has a dry cough that he can't get rid of.

We are looking for an efficient way to do this and have been reading up on furnace humidifier reviews. We will probably end up going with a humidistat.

Being able to control the humidity level like this certainly seems like the easiest and most efficient way to get the right amount of humidity in the air any time of the year.


My parents have a humidifier with a humidistat in their home. They love it! They've been homeowners for awhile, so they've experiences a few different types of humidifiers. They like this one the best, because it regulates the amount of moisture in the air.

One problem with some of the older humidifiers is that the air ends up being too humid. But if you have a humidistat, you can set the level yourself. Then the air in the home won't end up too dry or too humid.


@Azuza - That's scary. There are so many things in your house that can potentially make you sick. Of course, some people don't feel well if they go without a humidifier!

My sister has chronic sinus issues. If the air in her home is too dry, she feels horrible. Unfortunately, she lives in an apartment, so getting a Honeywell furnace humidifier isn't an option for her. She contents herself with a single room humidifier in her bedroom. She also makes sure to clean it thoroughly so she doesn't get sick from her humidifier.


When I was growing up, a friend of mine had a reservoir furnace humidifier in their home. Out of all the furnace humidifier types, I'm not sure why they chose this one, but that's what they had. Maybe there weren't as many choices back then, I don't know.

After they had the reservoir humidifier for awhile, the whole family got chronically ill. It took them quite awhile before they figured out what the problem was. It was a big mess. They eventually decided to just replace their furnace humidifier rather than having it cleaned. They didn't want to take any chances.


Can a furnace humidifier be installed on to any kind of furnace? I live in a very old house with a very old HVAC system and I'm just not sure that any model could be adapted to this


I have a couple of questions that I am hoping someone who has a furnace mounted humidifier can anawer. First and probably more importantly, what is the best furnace humidifier on the market? I don't have a ton of money to spend but I don't want to buy the cheapest model either.

Also, will it be possible for me to install the humidifier myself or will I need to hire a professional?


I really struggle with the dryness of the air in the wintertime and I just have to have a humidifier installed on my furnace to keep my home at a bearable level of humidity. Below at least a 50% relative humidity I start to have trouble breathing and my skin becomes very dry and cracked.

It was not that expensive to have a home furnace humidifier installed and the benefits have definitely been worth it. I used to dread the winters and would dream of moving to Florida. Now I can live in comfort all year long

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    • An ideal humidity level is about 45 percent.
      An ideal humidity level is about 45 percent.