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Do You Put Hot Or Cold Water In A Humidifier

Do You Put Hot Or Cold Water In A Humidifier? & Why?

Using a humidifier is an excellent solution to combating dry air. It would be a godsend for people living in arid regions or suffering from cough and allergies. Every humidifier needs water to work, but should you put hot or cold water in a humidifier?

Simply put, it is advisable to use cold water in almost every type of humidifier. It is safer for kids and pets, has less mineral content, and helps with extending the humidifier’s lifespan. 

Note that the cold water here doesn’t refer to icy water. It is the room temperature water we often get from the tap water supply.

In this post, I will explain why cold water is better for humidifiers, which type of humidifier can use hot water, and other related questions. You will have a better understanding of “adding cold and hot water to a humidifier.”

Why should you use cold water in a humidifier?

As I said, you should use cold water instead of hot water in a humidifier. Here are two main reasons for it.

Cold water is safer for children and pets

The importance of safety can never be overstated in terms of using a humidifier. It turns out to be even more crucial when you have kids or pets at home. 

Assuming you fill the tank with hot water, and then your kids continue to play around, they may knock over the humidifier at some point, causing burn and scald. Everyone doesn’t want to risk that. That’s also why you should be really careful when using a vaporizer.

On top of it, the hot water may spill on your hands or other places when filling the reservoir. It is very dangerous for seniors or people with weak hands. Vaporizers work by boiling the water, but the manufacturers don’t recommend adding hot water into it for safety considerations.

Cold water can extend the humidifier’s lifespan

Hot water contains more mineral content, which is often the culprit of humidifier issues.

The mineral buildup can be the natural breeding ground for mold and bacteria. If you are using a cool-mist humidifier, these microorganisms will get into the air, posing a health risk to family members. 

mineral buildup of humidifier

Warm mist humidifiers don’t spread germs, but the mineral buildups left in the tank will gradually clog the machine, leading to malfunction. 

To reduce the mineral buildup in the tank, distilled water is the best solution. If not, cold water can make the humidifier last longer than hot water.

Can I put hot water in a cool mist humidifier?

Can I put hot water in a cool mist humidifier

Cool-mist humidifiers have an array of advantages. They are safer, use less electricity, and are relatively cheaper.  

As the name suggests, it is designed to produce cool mist and isn’t embedded with any heating element. So adding cold water to it is the standard operation. 

You may wonder if you can put hot water in it. I will say the machine may still work as usual, but you shouldn’t do that.

Since hot water contains more mineral deposits, bacteria, and mold will thrive in the tank. As these components fling into the air with moisture particles, they will hunt for a new residence and get into our bodies. A part of the mineral content will also come out as white dust, adding extra work of dusting.

Molds and bacteria can lead to inflammation in our lungs. In addition, the warm mist may result in more white dust, adding extra work of dusting.

On the other hand, the parts of cool-mist humidifiers may not withstand the high temperature of the water, meaning that they may fail very soon, and the materials may release some harmful chemicals.

Even though many humidifiers these days are made with BPA-free plastic, they may contain other chemicals that are sensitive to high temperatures. 

These are the potential hazards you may get while adding hot water to a cool-mist humidifier.

Hot or cold water in a humidifier: which one is better for your health?

It is hard to give a single clear-cut answer to this question. In addition to the temperature of the water, it is also associated with which type of humidifier you have and how you use it.

When you put hot water into a warm mist humidifier, it will not damage the machine because the material can bear boiling water. It can even save some energy as you don’t need to heat the water from a low temperature.

Another upside is that all the minerals will not get into the air, and bacteria and molds will be killed by boiling water.

Hence, the warm steam from a warm humidifier is not harmful. Even better, the warm steam can help relieve the symptoms of cough, congestion, headache, and so on.  However, the extra mineral deposits in the tank due to the added hot water can be a nuisance, increasing your cleaning frequency.

You can get the same health benefits by putting cold water in a warm mist humidifier. It would take more time to get it boiled, but you can save some time cleaning the buildup off.

Cool mist also helps to alleviate some symptoms caused by dry air. No matter cold or hot water you add to a cool-mist humidifier, you can get the same health benefits and health risks, such as inflammation in the lungs due to the mold and bacteria in the water tank.

However, as we discussed above, adding hot water to a cool-mist humidifier is possible to make the appliance release harmful chemicals and more white dust. In this case, using cold water would be better.

Which type of humidifier is better for adding hot water?

Adding hot water to a warm mist humidifier will do no harm to the appliance itself but may let the user and family members run the risk of burning. However, it is much better than adding hot water in a cool-mist model.

There is a type of humidifier that prefer hot water – the whole house humidifier. The hot water can supplement the heat in the HVAC system, increasing the evaporation rate. So it would be best if you connected the humidifier to the hot water line.


For those who are not sure whether you should put hot or cold water in a humidifier, cold water is always your best bet.

It is safer for people who fill the water and the children and pets in your family. Meanwhile, it can make the machine last longer as it causes less buildup and damage to the parts of the device. 

You don’t need to use hot water, even if you use a warm mist humidifier. It can facilitate the heating process but will lead to extra work on cleaning the buildup layer and the potential hazard.

But there is one exception. You’d better use hot water with your whole-house humidifier. It can increase the evaporation rate, which is vital for improving the humidity level all over the house. 

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested more than 150 products in person, including humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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