How Exactly Does a Dehumidifier Work?

There are hundreds of different dehumidifiers out there to choose from, and I’ve reviewed what I think are some of the best. They all differ in capacity, energy consumption and features, but regardless of how different they are, they all function using the same basic principle.

I’m not going to bore you with a ton of technical talk. Instead, my aim with this page on my website is to explain how dehumidifiers work, so you can make an informed decision about which one will suit your needs best.

Humidity and Condensation

condensationDuring those hot summer months, the heat really can bear down on you. However, it’s not just because of air temperature, relative humidity also plays a role. Hot air has the ability to pick up a lot of moisture, and as it cools down it begins to release this moisture.

Here’s an example: Have you ever picked up a cold drink on a hot day? Of course you have! You’ll notice the can in your hands is wet, and that’s down to condensation.

As hot air comes into contact with a cool surface it begins to cool down, thus losing its ability to hold water. Having a vapor turn into liquid is known as condensation, and dehumidifiers take advantage of that basic principle.

Of course, there is more to it than that.

Dehumidifier Parts

The most common among dehumidifiers is the refrigerant type. They can be divided into these essential parts: a fan, compressor, cooling coils and the water tank. The fan pulls the air into the dehumidifier. The compressor (as indicated by its name) expands and compresses refrigerant which travels through the dehumidifier coils, cooling them down. The final piece of the puzzle is the water tank, or reservoir.

fan compressor and coilsAs the air gets sucked into the dehumidifier, it passes over the coils. Now would be a good time to remember that example with the soda can I told you about, because the air comes into contact with the coils and begins to cool down so it can no longer hold in moisture, and the process of condensation occurs. The water collects on the coils and drips down into the tank located below.

Since moisture free air is cold, it has to be re-heated before being introduced back into the room, and that’s why most dehumidifiers also have a re-heater. After the air is re-heated it is released back into the room.

Doing Away With the Excess Water

When it comes to getting rid of the water that’s collected by the dehumidifier, you have several options. Cheaper models only have a water tank which you have to empty yourself once it gets full. Most dehumidifiers have the option of shutting down automatically once the reservoir is full. Larger and more expensive models allow you to hook up the unit to a drain which gets rid of water continuously. With continuous drainage you can either let gravity do its job, or get a dehumidifier with a condensate pump.


Not all dehumidifiers have a humidistat, but I’m going to explain what it does and how it works since it’s a very nice feature to have. It can be broken down into two basic parts: a sensing element, and a relay amplifier.

Put simply, a sensing element consists of two metal conductors. A rise or drop in humidity creates an electrical resistance between these two elements. This resistance is picked up by the relay amplifier which decides whether or not to signal the unit to turn off the compressor.

Desiccant Dehumidifiers

desiccant and silicaDesiccant dehumidifiers function very differently. They have a desiccant material or silica gel which has the ability to capture moisture. They don’t have a compressor, tank or cooling coils, and the air doesn’t need to be reheated before it is released back into the room.

Desiccant dehumidifiers are effective in smaller spaces such as kitchens, bathrooms and closets.

To Sum It Up

If you took the time to read this article, it will help you navigate my reviews a little bit better because you won’t be stumped by all the technical terms. I can’t advocate one type of dehumidifier over another because I don’t know your situation, so it’s totally up to you. I just hope you’ve found the information above useful.

Back to Top
If you’re interested in how dehumidifiers work or you want one and are confused, take a look at my handy guide that tells you everything you need to know.