Informational Guide

Hot Or Cold Water In Humidifier?

You may think that hot mist humidifiers use hot water and cool-mist humidifiers need to use cold water. This is incorrect. Learn more with our complete guide.

by Josh M

When using a humidifier at home, it’s best to understand how your appliance functions. Many people wonder about the type of water that should be used with their humidifier, from hot water and room temperature water to cold water.

You might think that a hot mist humidifier would use hot water and a cool-mist humidifier would use cold water, but you would be wrong. In our guide, we will talk about why it is important to use room temperature or cold water with your humidifier.

Water is important to your humidifier because it is the fuel that allows your humidifier to work. Without water, you cannot add moisture to your environment. If you try to run a humidifier without water, it will shut down, and it may malfunction.

Dry air will move through the unit, but without water, dry air is all that will come out.

Depending on your humidifier, you may also feel that the air is hot because the internal fan mechanism has warmed the air a little bit. Most modern humidifiers come with an auto-shutoff feature that should override your humidifier and turn it off completely.

White Humidifier on Top of Bedside Table with Books

Do You Put Hot or Cold Water in a Humidifier?

Cool Mist Vs Warm Mist

In a cool mist or warm mist humidifier, the goal is to cool or heat the water temperature via an internal mechanism. It is not the initial water temperature that matters; it is the resulting water temperature that comes out of the device.

We recommend using cool or room temperature water with every cool mist or warm mist humidifier.

Whole House Humidifiers

Unless you have an Aprilaire humidifier, we recommend using cool water or room temperature water with your whole house humidifier. Cool water can help your humidifier last longer and keep internal pieces of the device cleaner longer.

Furnace Humidifiers

A furnace humidifier is used to help heat a room as well as add humidity to the air and often is connected to a hot water line. These humidifiers tend to be more difficult to install and may require a professional for proper installation.

With a furnace humidifier, it is typically advised to use hot water with the appliance. However, look to the manufacturer’s instructions to be sure.

Bypass Humidifiers

A bypass humidifier should also use hot water and tends to follow a similar setup to a furnace humidifier. We recommend using an HVAC professional because most bypass humidifiers must be connected directly to a hot water source and heat pump in the home.

These appliances work by taking warm air, moving it through one of the humidifier ducts, bringing it back to the furnace, and then blowing the air back out into the room through the furnace.

Humidifier for Good Sleep

Common Mistakes When Using Humidifiers

The most common mistakes that homeowners make when using humidifiers include the following:

Letting the Humidity Rise Too High

Humidifiers help to raise the humidity levels in your home. They do not reduce humidity levels. A common mistake homeowners make is allowing the humidifier to run 24/7 and not monitoring the humidity level in the house.

Most humidifiers will enable you to set a maximum level, which keeps the humidity from rising too high in the home. We recommend purchasing a unit that allows you to set a level, so you avoid mildew and mold growth from too much humidity.

Ignoring Levels of Humidity at Home

Too many homeowners forget to monitor the humidity levels. If you do not monitor the humidifier levels, it is easy for the room to become too saturated with water droplets. High humidity levels can lead to bacteria, germ, mildew, and mold growth.

Make sure that you choose an appropriate level of humidity and check to ensure that the reading remains at or below that appropriate level.

Using Tap Water for Humidifier

Using tap water for your humidifier is typically okay, but we recommend using distilled water for your humidifier. Why? Using tap water increases the likelihood of all the nasty bacteria and germs multiplying in your humidifier.

If you use distilled water, you can keep your humidifier cleaner and keep your home healthier.

Not Cleaning The Humidifier Often

If you wait too long to clean the humidifier, then the overgrowth of bacteria can create illnesses at home. Make sure that you unplug your humidifier when cleaning it to avoid electricity and water mixing.

Make sure that you also check the bottom of the humidifier for standing water and keep all exterior surfaces clean and dry. Learn more about changing filters here.

Letting Water Sit-In The Humidifier Too Long

No one wants to deal with bacteria, mildew, or mold growth at home. If you let water sit too long in the humidifier, however, this is exactly what will happen.

If you run your humidifier daily, then we recommend cleaning your water reservoir once per week and cleaning your entire unit once per month. Letting the water sit without a thorough cleaning is the best way to create a build-up of bacteria.

Dehumidy Room

People Also Ask (FAQ)

What do you use in an Aprilaire humidifier, hot or cold water?

An Aprilaire humidifier can use several different water options, including hard water, cold water, hot water, and soft water. Hot water is the best option for an Aprilaire humidifier because they use heat to create the evaporation that increases the humidity levels.

Can you put ice in a cool-mist humidifier?

You can put ice in a cool-mist humidifier to help cool the room, but we recommend avoiding this process because higher humidity levels tend to make rooms feel warmer/hotter.

Using a cool-mist humidifier will raise the humidity levels in the room so the cooler mist won’t cool the room down effectively. We recommend using an air conditioner unit instead.

What happens if you don’t use distilled water in the humidifier?

Using distilled water in your humidifier is the best way to avoid bacteria growth, mold growth, and the white powder that often accompanies humidifiers.

However, most humidifiers work with any type of water, and you can use regular tap water if that is what you have available at home. Make sure that you thoroughly clean your humidifier weekly if you use tap water.

How do you make distilled water at home?

Making distilled water involves boiling water for approximately 45 minutes while consistently adding ice to the pot that you are boiling the water in. From here, the steam should cool down and return to the pot as water. Mineral residue should be left behind.

What can I put in my humidifier to kill bacteria?

We recommend cleaning your humidifier with hydrogen peroxide. You can add a few drops to your water reservoir each month to help keep it clean. You can also add a single cup of white vinegar to help prevent bacteria growth.


Taking care of your humidifier properly involves cleaning it regularly as well as using room temperature or cold water when refilling the tank. We recommend cleaning your humidifier thoroughly at least once per month to avoid bacteria build-up.

Last Updated on July 16, 2021

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.