Informational Guide

How Do Dehumidifiers Work?

We look at the different types of dehumidifiers, the pros and cons of each, and show you exactly how they work in the home.

by Josh M

Damp, humid conditions can bring all manner of issues into your home. Thankfully, dehumidifiers exist to help you regulate your air quality, but what exactly does a dehumidifier do and how does a dehumidifier work?

Over the years I’ve used all kinds of dehumidifiers to solve a wide range of problems. In this guide I’ll show you how different dehumidifiers work, the benefits of using one, and help you determine whether you would benefit from one in your home.

What Is Humidity?

Dehumidifiers help deal with humidity in your home, so it’s important to know what humidity is. Humidity is the amount of water vapor in the air. This is often described as the relative humidity in an area or a room.

The higher the relative humidity, the more moisture there is in a room. A damp room will have a high relative humidity, whereas a room why dry air will have a low relative humidity.

Why Does Humidity Matter In Your Home?

So why does relative humidity matter? Well, if your air is too humid and has too much water vapor then it can lead to the development of harmful bacteria, viruses, mold, dust mites, and other harmful pollutants. This can lead to some serious health risks if there’s no moisture control in place [1]. High humidity can also damage your home and belongings.

Low humidity can also cause discomfort, triggering some allergies and leaving your throat, nasal passages, and eyes itchy [2].

The optimal relative humidity in your home is around 30-50%. Removing excess moisture, but not overdrying the air is the key to protecting your health, your home, and your comfort. This is why dehumidifiers and humidifiers are increasingly popular.

What Exactly Is a Dehumidifier?

Dehumidifiers remove excess moisture from the air. They do this by drawing in air filled with water vapor, removing some of the moisture as liquid water, and then blowing dry air back into the room. This lowers the overall relative humidity in a given area.

There are several ways this is accomplished, including electrical, mechanical, and natural methods. Most dehumidifiers are electrical, and many people have a portable dehumidifier in their homes. By dehumidifying or removing humidity, these devices can make our lives more comfortable and help to protect us and our belongings.

Dehumidifiers Vs. Air Conditioners

An air conditioner is used to cool a room down, whereas a dehumidifier is used to remove excess moisture from a damp room.

Even though they have different functions, in many cases, a central air conditioner also removes moisture and humidity from the air. However, the process uses more energy and makes the system run longer to cool the air after it has been devoid of moisture. By using a dehumidifier with the AC, you can run the units for shorter times and make the AC more efficient, saving on your annual energy bills.

Dehumidifier Components

Mechanical and electronic dehumidifiers may all use slightly different processes, but the parts are usually the same. Here are the key components which come together to create a dehumidifier:

  • Fan.
    The fan is either a dual purpose (when there is a single fan) or a single purpose (when there are multiple fans). The main job is to bring air from around the unit inside to be cycled through and to force the dehumidified air out into the room.
  • Compressor.
    The compressor works much like a compressor in an air conditioner. Its job is to compress and cycle the refrigerant through the coils.
  • Reheater.
    The cooling process from the refrigerated coils causes heat to be removed from the air. The reheater collects the excess heat and returns it to the air after it has the moisture removed.
  • Compressor Cooling Coils.
    The cooling coils cool and decompress the refrigerant, allowing the moisture to accumulate and stay out of the air.
  • Reservoir.
    Finally, the reservoir is where the collected moisture/humidity from the air is stored. The collected water will either be evaporated by the reheater, collected in silica gel, or drained through a drain hose.
  • Humidistat
  • Modern dehumidifiers have a built-in humidistat that measures the moisture levels in the air. This controls when dehumidifiers work to remove moisture from the air, and when they can stop. This component is essential for keeping the relative humidity of your air within acceptable levels and helps to improve the overall energy efficiency of the dehumidifier.

Origins & Working Principles of Dehumidifiers

The first dehumidifier was invented by Willis Carrier in 1902 and the dehumidifier’s first job was to remove moisture and (hopefully) odors from a New York printer’s warehouse. Carrier said that this invention was the basis for his other air conditioning inventions and led to the brand name we all know today.

The first dehumidifier was crude, of course, and used a series of cold coils, a warm coil, and fans to move air through different temperatures to remove the moisture. Today, the process isn’t much different, but it is a lot more advanced.

The main idea behind a dehumidifier is to absorb moisture or extract excess moisture from air molecules. It can do this in a few ways, but the most efficient is to rapidly cool the air so that the water molecules become too dense to stay in the air molecules. We see this process frequently with window condensation as cool air hits a cold surface.

The moisture is then removed and collected. The super-cooled air is heated back up and warm air is returned back to the source, room, or home.

Main Types of Dehumidifiers: Which Will Work for Your Home?

There are 3 main types of dehumidifiers:

Refrigerant Dehumidifiers (Compressor Dehumidifiers)

Refrigerant dehumidifiers work using refrigerant gas which moves between a cold coil and a warm coil, changing from gas to liquid and back to gas. Moist air is drawn in using a fan and comes into contact with the cooled coils. The water condenses and drops down into a water reservoir, while the air passes through the warm coils and heats back up. The dry air is then released back into your home.

Refrigerant dehumidifiers are the most common type of dehumidifier. They are often used in areas with high humidity because they can extract moisture quickly, and you’ll find portable models and fixed installation models with continuous drainage.

Refrigerant dehumidifiers are usually inexpensive and cheap to run (depending on the energy factor and energy star rating), but they can’t be used in very cold conditions as this can cause the cold coil to freeze over. This means they aren’t always suitable in cold basements, garages, or cellars.

Desiccant Dehumidifiers

Desiccant models work using water-absorbing material to collect moisture, this is usually absorbent gels, silica beads, or salts. Humid air is drawn over the material and as the air cools moisture is collected. Dry air is then blown back into the room.

Once the absorbent material is full you will need to either replace the pouches, recharge them, or replace the entire dehumidifier device. Plug-in models use an electric coil to heat the silica and evaporate the moisture so they can be used again. Other types can be put in the microwave or oven to heat the silica.

One-time desiccant models are fairly cheap and are great for small areas like inside your kitchen cabinets. This type of dehumidifier will work in cold conditions because there are no cooled coils to freeze over.

Whole House Ventilation Dehumidifiers (Furnace Dehumidifier)

Whole home dehumidifiers are much larger and used for homes with a constant moisture problem. These are generally installed in a basement or crawl space and connected to the home’s ventilation system.

As the air goes through the furnace portion of the dehumidifier, the moisture is removed, the air is reheated and as the warm air contracts it’s put back into circulation through the home vent system. They are usually plumbed in so that there is continuous drainage of the gathered liquid water.

These systems can be expensive and require professional installation but they can remove a lot of moisture from the air. They are ideal for large homes with high humidity, flooding, or foundation seeping issues and can also be used for crawl spaces, basements, or even commercial areas that have more moisture and need extra dehumidifying steps.

How Does A Dehumidifier Work? Step By Step Process

Compressor Dehumidifiers (Refrigerant Dehumidifiers)

  1. A fan, or series of fans, brings in warm air through the sides, back, or bottom. Wall and ceiling-mounted dehumidifiers will have different intake and exhaust points than portable models.
  2. Warm air containing moisture is directed through a series of cold coils filled with refrigerant gas.
  3. The fan compressor keeps the pressure of the refrigerant high within the cold coils. This keeps the copper tubing cold.
  4. The warm air cools as it comes into contact with the cold coils and the moisture condenses on the evaporator fins within the dehumidifier.
  5. A reheater is used to warm the air back to room temperature, and the dry air is released back into the room.
  6. The dehumidifier collects the liquid in a water tank or collection tank ready to be emptied. Larger dehumidifiers will be plumbed in for continuous drainage.
How a Dehumidifier Works

Desiccant Dehumidifiers

  1. Desiccant models either use a fan to direct air into the device or they are placed somewhere the air flows naturally.
  2. As the humid air is brought into the fan, the dehumidifier works by directing it over a moisture-absorbent material. Usually, this is silica salt.
  3. Moisture is extracted from the air as it passes over the material.
  4. The dry air is then heated and released back into the room
  5. These dehumidifiers work without a water tank. When the moisture-absorbent material is full then it is either dried out by heating it, or replaced.
  6. Reusable desiccant dehumidifiers have moisture-absorbent material which can be used for years.
Disposable Dehumidifier

Furnace Dehumidifiers

  1. Furnace dehumidifiers or whole-home dehumidifiers work like other refrigerant-based dehumidifiers, but on a larger scale
  2. The dehumidifier is installed into the HVAC system with input and exhaust vents connected to ducts
  3. Air is drawn in through the intake line and passed over cold coils
  4. The dry air is then directed to the air handler to be heated or cooled for distribution around your home
  5. The moisture collected is drained through fixed plumbing
Furnace Dehumidier Installation Sample

Natural Dehumidifiers: How They Work

A natural dehumidifier is a smaller model that usually comes in a canister, box, or as a disposable unit. These generally have very little power consumption and are the more energy-efficient type of dehumidifier.

These are the most common natural dehumidifiers:

  • Charcoal-Based Dehumidifier.
    Charcoal is a porous material that naturally absorbs moisture from the ambient air. You can use briquette or lump charcoal to reduce humidity and absorb odors in a room.
  • Salt And Essential Oil Dehumidifier.
    Salt is another natural absorbent and can be used as a dehumidifier. A common DIY project is to create a salt bucket to collect moisture and add essential oils to help purify odors.
  • Baking Soda As A Dehumidifier.
    Baking soda works a lot like charcoal to absorb odors and moisture from the ambient air. You can find baking soda boxes with removable panels to allow airflow without having to open the container.
  • Clay-Based Dehumidifier.
    Clay is a commonly used dehumidifier that is cost-effective and non-corrosive. If you don’t want to use a salt bucket, desiccant clay is a suitable alternative.

Benefits Of A Dehumidifier

Helps With Allergies

Allergens thrive in moist air, and with a proper humidity level, many of the allergens in your home can be controlled. By using your dehumidifier to maintain a humidity level between 45 and 50%, you can prevent mold and mildew from growing and limit the pollutants which trigger allergies.

Reduces Pest Related Problems

Like mold and mildew, other pests such as spiders, roaches, and even dust mites require moisture to survive. If you remove the humidity from the home, these pests won’t have the required moisture for hydration and will either die out or move on. In fact, dust mites will be largely destroyed if you use your dehumidifier to keep the humidity below 65% [2].

Controls Moisture Levels

Your dehumidifier works to control the indoor humidity levels in your home. You can make your dehumidifier work in hot or cold conditions and it will help to keep you comfortable at home. Lowering the humidity to between 40 and 60% in your home will help you breathe easier and stay more comfortable year-round.

Protects Your Health

Along with normal moisture levels in the air, it also makes things more comfortable. Humid air is harder to breathe, and if the humidity is too high, it can also lead to illness and respiratory issues.

Reduces Energy Costs

You can also make your dehumidifier work to lower your bills. By using a dehumidifier instead of a dehumidifier you can lower the humidity and tackle moist air without spending as much on electricity.

7 Signs You Need A Dehumidifier

Here are the clear signs that you may need a dehumidifier, but if you aren’t sure then you can use a hydrometer to measure the relative humidity in the air.

  • There’s visible condensation on the walls
  • You can see mold or blistering paint
  • Clothes won’t dry because of a damp problem
  • There’s a musty smell
  • The room is cold and damp or feels very hot and clammy
  • You’re sneezing or coughing more frequently, or finding it harder to breathe
  • Creaky floors or doors which have expanded because of the moisture

How Long Does It Take For A Dehumidifier To Work?

You should run your dehumidifier for at least 12-15 hours to have the most impact. You may need to run it for longer if you have a lot of humidity, but you may need to empty the tank. You should expect it to take at least 12 hours before you notice the effects of your dehumidifier.

Some larger models, whole-home dehumidifiers, and small silica-based models may start working immediately. However, you are unlikely to notice the effects of the lower humidity in the areas they are located in (a basement, inside your cabinet, etc.) until the drier air begins to circulate.

It will also depend on how humid the air inside your home is, the airflow rate, and the ventilation situation.

Optimal Dehumidifier Humidity Setting

Most dehumidifiers have setting controls which let you choose the desired humidity level. On average, though, you should strive to maintain a humidity level between 40 and 60%. 45 to 50% is considered the “sweet spot” for health, comfort, and limiting mold or pest growth.

However, you should always make your dehumidifier work for you so don’t be afraid to experiment with different humidities to see which is the most comfortable. You should also consider the energy efficiency and only use a dehumidifier when it’s needed.

What Is the Difference Between Humidifiers & Dehumidifiers?

A humidifier and dehumidifier are opposites. The primary difference is that a humidifier adds moisture as the air passes through while a dehumidifier removes moisture from the air.

Humidifiers are best used when the air is drier, humidity levels plummet, and the seasons turn colder. Late fall and winter are when you will find most humidifiers in action.

A dehumidifier is best utilized when the air is full of moisture, there’s a higher temperature, and allergens that cause respiratory illness are at their peak. You will find dehumidifiers best used in spring and summer to stop mold growth and keep you comfortable.

People Also Ask (FAQ)

How much do dehumidifiers cost?

A good quality dehumidifier will cost $50-$200, but the exact cost will depend on the size dehumidifier you choose, and the make and model of the appliance. Some whole home models can cost over $1500, plus installation costs.

Where should you place a dehumidifier?

The best place to put a dehumidifier is as close to the source of moisture as possible. To improve the dehumidifier’s efficiency you should try to place it in the centre of the room to maximize the air flow in and out of the device.

How long does a dehumidifier usually last?

A dehumidifier will usually last 5-10 years if it’s properly cleaned and maintained. However, the more you use a dehumidifier, the quicker it will need to be replaced. Portable dehumidifiers usually last 3-5 years.

How can I check humidity levels in my house?

You can use a hygrometer or humidistat to measure the humidity in your home. Many dehumidifiers have a hygrometer built-in, but you can buy them separately from places like Amazon or Sylvane.

Do dehumidifiers cool you down?

Dehumidifiers will not lower the temperature in a room like air conditioning devices, but because a dehumidifier removes humid air it can make you feel cooler and more comfortable.


Dehumidifiers remove moisture and humidity from your home which can help to improve the air quality, stop allergens and pollutants from impacting your health, and protect your home and belongings.

Hopefully, this guide has explained what a dehumidifier does why you might benefit from using a dehumidifier.





Last Updated on January 24, 2023

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.