How Does a Cool Mist Humidifier Work?

In two of our previous articles (what is an ultrasonic humidifier and how does an ultrasonic humidifier work), we already introduced you to the concept of humidifiers, what do they do, and why you should use an ultrasonic humidifier.

In this article, we want to talk about another type of humidifier: the cool-mist humidifier.

To give you a brief reminder, humidifiers are often used in indoor spaces to enhance indoor humidity. Dry air may be an underlying reason for many health issues, especially respiratory ones.

Furthermore, during the winter days, even the cool-mist humidifiers (not just the warm-mist ones) can help lower your electricity bills, as humid air tends to make the indoor space feel warmer. On the other hand, during warm days, if you are using a cooling unit along with the humidifier (air condition, or the whole house fan), you can also expect some cooling effects.

When it comes to buying a humidifier for your home, it all comes down to your personal needs. You usually want to align the size of the room to the size of the humidifier, and include some features that you find particularly important.

However, if you’re not sure where to start, perhaps consider this distinction first: do you want a cool or cold mist?

The cool and hot mist are two broad categories of humidifiers, where one boils the water before dispersing it into the air, while the other one, as the name says, disperses the cold water either via ultrasonic vibrations or by evaporating the water particles into the air with a fan or a rotating disc.

So, how does a cool-mist humidifier work?

Keeping the Room Cool and Moist

If you’re looking for a way to keep your room fresh and the air moisturized, a cool-mist humidifier is probably the right choice for you. This is often the case with people living in warm climates with dry air. The combination of making the air a bit more humid along with cool is the best possible option in such scenarios.

There are two types of cool-mist humidifiers. We already talk about one in two of our previous articles, the ultrasonic humidifier, so we recommend you to check it out on our blog. The others are in the evaporative wick and the impeller humidifier, and we are going to focus on those two types now.

But before we jump to explain the actual mechanism of how the evaporative humidifier works, let’s see what are the most crucial differences between the ultrasonic, the evaporative humidifier, and the impeller humidifier.

The Noise

While the ultrasonic one may be ideal for the bedroom or the children’s room, some people actually prefer to sleep next to some kind of white noise, which is why they opt-in for the evaporative humidifier in the end. The evaporative one for sure is the loudest, however, its noise is not so unpleasant, as it quickly merges into the background. The impeller humidifier is considered slightly less noisy than the evaporative one, however, its noise is considered more unpleasant, as it produces clearly mechanical noise with its rotating disc.


Since these units usually don’t have a filter, you don’t need to bother about that, however, regular cleanings are needed in order to prevent mold and bacteria growth inside their buckets. In the case of the evaporative humidifier, you should also clean the fan, and in the case of the impeller humidifier, you should clean both its dish and the disc.


The evaporative humidifier is by far the cheapest, although the price difference is only between $10–$50. The ultrasonic is probably the most expensive one, due to its main benefit – that it’s completely silent. However, cool-mist humidifiers are generally cheaper than warm-mist ones, and they also spend less electricity.


Setting up any of the given units to work is fairly easy and simple. All you need to do is pull out the reservoir and fill it up with water. Then, place the appliance in the middle of the room, or if not in the total middle, at least position it some 1-3 feet away from the wall. Otherwise, you risk damaging the wall with the moisture being expelled from the unit.

In case you decide to purchase an evaporative unit with a filter, you should also read the instruction manual in detail to figure out how to replace the filter, otherwise, all you need to do is to clean the dish and the propellers frequently.

Basically, none of the three types of humidifiers has a special advantage or disadvantage when it comes to operating them.


Thanks to their simple technology, you can expect the humidifying unit to serve you for a couple of years. Their pieces don’t break or glitch easily. The usual lifespan of any of the humidifying units is 4 to 5 years. If you maintain them really well, you can expect them to work even longer. Nevertheless, regardless of how careful you are, you can still expect your humidifier to form some mineral deposits that may be difficult to remove. In case this happens, you should rather consider purchasing a new device than continue with the old one.

How Does the Evaporative Humidifier Work?

The evaporative humidifier is also the most common type of cool-mist unit you can find. They have been around for decades, and people still pick them as their first choice very often, meaning that they are giving good results.

If you decide to purchase a portable evaporation unit, you can expect it to be a bit larger in size. The wick filter that they use is also quite large usually, which is why these models occupy more space. Of course, there are certain designs that are smaller in size and more appropriate for smaller rooms.

This type of humidifier works in a similar way as if you’ve placed a jar full of water into the room and let it evaporate, but with an extra something – the fan.

The unit has a dish that you need to fill with water. The best possible option is to use distilled water, as otherwise, you risk the formation of white dust around your home, depending on how hard the tap water is in the area where you live (how high the concentration of mineral contents). The internal fan on the unit then pulls the air inside and the air then flows past the wick filter. The wick filter is also absorbing water through a reservoir. The air becomes wet and gets propelled out with a fan, making the room air more humid quickly and efficiently. This continues until the point in which the optimal humidity level is reached.

Some evaporative units actually have a filter that needs to be replaced from time to time. However, if you want the most environmentally friendly solution, you can easily find units without the filter.

There is also aromatherapy as an additional feature of the evaporative humidifiers. You may find this a good option if you also wish to add some nice scent to your indoor air.

Another benefit to using the evaporative humidifier is that it’s perfectly safe for everyone to use, as long as you clean it regularly and prevent the formation of bacteria and mold. Since it doesn’t heat up, you can freely use it in your children’s room, as there is no danger of burning.

By using only distilled water, you will also avoid spreading the mineral content of tap water around and collecting white dust on your furniture.

How Do Impeller Humidifiers Work?

The basic principle of this humidifier is very similar to its counterparts, as it all comes down to spreading the cool water particles into the indoor air. What’s different about them is that they have a disc that rotates and throws the water from the dish to a diffuser.

This process leads to breaking the water into small drops that then keep on floating in the air in the form of mist.

Similar rules apply to this unit as well. You need to keep the dish where the water goes clean, as otherwise you risk collecting mold and bacteria. Also, if your tap water contains high levels of minerals, you should consider using distilled water only.

A good side of this unit is that the mechanism it uses is very simple, so there is a low chance of disfunction. Even if something stops working, the parts are not complicated and it should be fairly simple to fix. The caveat is the noise it makes, as it’s not as loud as the evaporative unit, however, it’s not very pleasant if you plan on sleeping next to a working device.

Final Word

Depending on what you want from your humidifying unit, you can pick between the warm and cool-mist units, however, you should keep in mind that cool-mist units are more environmentally friendly, cheaper, spend less electricity, and are safe to use also around pets and children.

If you’re looking for a simple and elegant solution for your dry indoor air problem, a cool-mist humidifier will likely address all of your issues.

But which one to pick? Well, it depends on what do you want to achieve. If you don’t mind a bit of white noise and want to pay less money, the evaporative unit should be the right choice. It’s been on the market for a long time and usually costs less than its counterparts.

On the other hand, the impeller humidifier is a good choice too, as you can expect it to last longer thanks to its simple operating mechanism.

Finally, the ultrasonic unit is the most expensive usually, but it’s also the quietest one and doesn’t have a filter.

In order to combat the potential dust, most, and bacteria formation, make sure to use distilled water instead of tap water and clean your unit frequently. When you notice that it’s starting to be impossible to remove the mineral contents from the dish, it means that it’s time to replace the unit.