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

While doing any type of research to improve energy efficiency, indoor air quality (IAQ), or humidity reduction in your home, you have learned about dehumidifiers. But, exactly how does a  dehumidifier work?

Do they work differently in the bedroom compared to a dehumidifier in the basement?

Can you use a dehumidifier in your garage?

In this article, we will examine the different types of dehumidifiers, their pros and cons, and get down to the details to show you exactly how they work. Armed with this new knowledge, you will be able to make a well-informed purchasing decision.

In essence, a dehumidifier is a machine or process that removes moisture from the air. There are several ways this is accomplished, including electrical, mechanical, and natural methods.

If you were to break the word down, it tells you exactly what it does. By dehumidifying or removing humidity, these devices can make our lives more comfortable and even save money. In many cases, a central air conditioner also removes moisture and humidity from the air.

This process, though, 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.

Mechanical and electronic dehumidifiers use different parts to function properly and remove the humidity. Let’s break down the common parts now.

  • 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 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. It will either be evaporated by the reheater, collected in silica gel, or drained through a drain hose.

Origins & Working Principle of Dehumidifiers

Like many air conditioning and home climate control devices we know and use today, the dehumidifier has a long history. Invented by Willis Carrier in 1902, the dehumidifier’s first job was to remove moisture and (hopefully) odors from a New York printer’s warehouse.

Carrier has said that this invention was the basis for his other air conditioner inventions and led to the brand name we all know today.

The first dehumidifier was crude, of course, and used a series of coils 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.

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

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

As we have touched on so far, there is more than one type of dehumidifier. The three major types are refrigerant-based, whole home, and desiccant-based. Let’s take a closer look at all three.

Refrigerant Dehumidifiers (Compressor Dehumidifiers)

Refrigerant based systems work very similarly to a portable air conditioner. They are generally portable themselves and use a fan to pull air in over coils to cool the air and remove humidity.

Once the moisture is removed, it is collected in a reservoir tank that needs to be emptied, or is automatically removed through a drain line. These models are best for smaller areas, or specific uses, such as seasonal or when you are ill.

You will also find these used most often in bathrooms with lower ventilation and even in kitchens where humidity rises quickly.

Desiccant Dehumidifiers

Desiccant models use absorbent gels or salts to collect moisture. You will generally find silica beads or grains inside pouches that absorb the moisture. Once they are full, you will need to either replace the pouches, the entire dehumidifier device, or plug it in.

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 use options are fairly cheap and are great for small areas like inside your kitchen cabinets. You can also use them in gun safes, vehicle cabs, and other areas that are difficult to maintain.

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 put back into circulation through the home vent system.

These systems can be expensive and require professional installation. However, they are ideal for large homes with high humidity, flooding, or foundation seeping issues. For crawl spaces, basements, or even commercial areas that need the extra dehumidifying steps, these systems may be the best option.

How Does A Dehumidifier Work? Step By Step Process

Dehumidifiers work in different ways based on how they are constructed, powered, or even used. Let’s break each type down, step by step, to see how they work.

Compressor Dehumidifiers

For these models, a fan will bring air in from the sides, back, or bottom. Wall and ceiling mount options will have different intake clearances and locations that floor mount or portable models. The warmer, moist air will be taken through a series of refrigerant-filled coils.

The compressor keeps the pressure of the refrigerant high inside the coils, which makes the copper tubing cold. This causes a heat transfer from the air to the coils and, in turn, causes the moisture to condensate on the evaporator fins inside the machine.

In most cases, a reheater is used to warm the air back to its original temperature (minus the moisture) and return it to the room. The condensate collects in a drain pan or moves through a drain hose out of the home.

How a Dehumidifier Works

Desiccant Dehumidifiers

Desiccant types work in a couple of different ways, though the process is similar for each. These are mainly considered passive or absorbent dehumidifiers because there aren’t a lot of moving parts.

Instead of a fan to move the air in and out, these smaller types are found in cabinets, on countertops, or in bathrooms on the shelf to absorb moisture from the air that happens to pass by. They don’t actively pull in moist air.

Over time, natural air movement will bring the humid air to the device, where a natural or man-made material will absorb the moisture as the air passes through. Usually, a silica salt or other reusable material is involved.

Once the material is full, though, is when the differences take over. Disposable models are simply removed from the home. Electric models get plugged in to heat up the desiccant, removing the collected moisture and allowing them to be used again.

Some types are placed in a microwave or oven to remove the heat from the desiccant, too, which can take several hours. Once dry, though, these can be reused over and over for several years.

Disposable Dehumidifier

Furnace Dehumidifiers

Furnace models or whole-home dehumidifiers work the same as a portable unit, just on a much larger scale. They are permanently installed within the home’s HVAC system, and the input and exhaust vents are connected to the existing ducting of the home.

When the system is on, the air is moved through the air intake through the dehumidifier. In almost all cases, this is first. The air is dried with some exhaust going to the crawl space or basement before heading to the air handler to be heated or cooled for distribution to the rest of the home.

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. Several types accomplish the same thing, but let’s see how each one works.

  • 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 adding 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.

What Is A Dehumidifier Good For?

We all know by now what dehumidifiers do, but what is the importance of drying the air? Let’s look at the most important aspects of maintaining the proper humidity levels in your home.

Helps With Allergies

Allergens are one of the most common in-home issues we face on a daily basis. Everything from seasonal allergies to respiratory issues like bronchitis or asthma can be traced back to allergens in the home.

With a proper humidity level, many of the allergens in your home can be controlled. Maintaining a humidity level between 45 and 50%, for example, will prevent mold and mildew from growing. With the right dehumidifier, you can dial in the humidity level you need based on your individual situation to get the level of protection you need.

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.

While it is unlikely that simply lowering the humidity can get rid of an infestation, maintaining the correct humidity levels will help prevent them from forming in the first place.

Controls Moisture Levels

Obviously, the biggest factor is controlling the indoor humidity levels. It doesn’t matter if it is a hot summer day or a cold winter night. Humidity in the home can make things unbearable. With a dehumidifier at work, the moisture levels in the air you breathe will be regulated to normal levels.

Improves Comfort

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.

Lowering the humidity to between 40 and 60% in your home will help you breathe easier and stay more comfortable year-round.

Reduces Energy Costs

Because the air is drier, the air conditioner in your home has to work less. Because of the condensation coils in an evaporator, ACs are natural dehumidifiers. However, they have to work harder when humidity is high.

An AC running longer and working harder only increases your energy bill. Running a dehumidifier will help the AC be more efficient and require fewer cycles to maintain the temperature in your home.

How Long Does It Take For A Dehumidifier To Work?

A lot will depend on the type and size of the dehumidifier you have to determine how long until you notice the effects. Most dehumidifiers will take between 8 and 12 hours to dial in and start being effective.

However, larger models, whole-home dehumidifiers, and small silica-based models actually 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. As a good base number, though, you should expect about 12 hours to notice the effects of your dehumidifier.

Optimal Dehumidifier Humidity Setting

Many in-home dehumidifiers will have a control setting that lets you choose the desired humidity level. This is one control that should not be overlooked. Too much humidity will cause mold growth, invite pests and make the air harder to breathe.

Likewise, not enough humidity and you will get dry skin, chapped lips and could develop breathing problems. So what is the ideal dehumidifier setting? The answer lies in the type, size, and location of your dehumidifier.

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.

What Is the Difference Between Humidifiers & Dehumidifiers?

As you can probably surmise, a humidifier and dehumidifier are opposites. Of course, the primary difference is that a humidifier adds moisture to the air while a dehumidifier removes moisture from the air.

Each one has its place and time of use, as well. For a humidifier, they 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, on the other hand, is best utilized when the air is full of moisture, the temperature is hotter, and allergens are at their peak. You will find dehumidifiers best used in spring and summer.

People Also Ask (FAQ)

How much do dehumidifiers cost?

The initial cost of a dehumidifier will depend significantly on the type and size. Natural dehumidifiers are fairly inexpensive and can be found for a few dollars each. Portable units are most common, and there are many sizes and styles to choose from. You can expect to pay between $50 and $200 for a decent to high-end model. Whole home models will vary in cost based on size, location, and installation method, but the average cost can easily exceed $1500.

Where should you place a dehumidifier?

The best place to put a dehumidifier is central to the room. However, you also want it out of the way, so you don’t trip over it or walk into it. For these reasons, a central room of the home in an out of the way place is ideal. As long as clearances are met and there is proper airflow, a corner or side of the room is acceptable.

How long does a dehumidifier usually last?

With proper care, maintenance and cleaning, a dehumidifier can last you a long time. Mid-range and high-end models will easily last a decade or more. After this time, though, you will notice that productivity begins to decline. When looking for a new model, you should expect a solid 10 to 12 years of constant use, though.

How can I check humidity levels in my house?

The only real way to test the humidity level of the home is to invest in and use a hygrometer. These inexpensive tools will measure the air temperature and humidity levels and give you instant results for the room you are in. Some higher-end dehumidifiers will have a hygrometer built-in. Otherwise, you can buy them separately from places like Amazon or Sylvane.


Whether you need to remove humidity and moisture in a single room or the entire home, there is a dehumidifier model for you. Small spaces like kitchen cabinets, gun safes, and lockers can use natural dehumidifiers like clay, baking soda, or silica.

Whole rooms such as bathrooms or bedrooms, though, will need larger units. Portable dehumidifiers are ideal for these situations. And, of course, the whole-home furnace style dehumidifiers are ideal for wet areas such as crawl spaces, your basement, and the entire home.

Hopefully, you now have a better idea of the types of dehumidifiers, how they work and which is best for your needs.

Last Updated on September 2, 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.