How Does a Dehumidifier Work?

By: Debbie Wolfe | Affiliate Disclosure

Indoor air can hold a lot of water vapor and high humidity levels can make an area feel extremely uncomfortable. High humidity can also lead to property damage, mold, and mildew. Though your home air conditioning unit naturally removes moisture, there are situations where you may need a portable unit to remove excess moisture. That’s where a dehumidifier comes in: a dehumidifier reduces and regulates the amount of moisture in the air.

Types of dehumidifiers

Dehumidifiers come in several sizes and price ranges. They are versatile machines that can be used for single rooms, basements, apartments, or large commercial areas. The type of dehumidifier you choose will depend on your budget, home, and needs. Here are the most common types:

  • Refrigerator-style dehumidifier—This dehumidifier works by removing excess moisture from the air by cooling it first. It pulls in warm air, then passes it over cooling coils. The moisture condenses and drops into a water collection tank. Then, the dried cool air is blown back into the space by a fan.
  • Desiccant dehumidifier—Great for cold environments, a desiccant dehumidifier works by taking in air and passing it over some type of desiccant material, like silica gel. The desiccant substance absorbs moisture and removes water vapor from the air.
  • Portable dehumidifier—This is the most common type of dehumidifier. Portable dehumidifiers are meant to be used in a single room and aren’t designed to dry the air in an entire house.
  • Whole-house dehumidifier—This centralized unit works much like an air conditioner. It’s a fixed unit capable of removing excess humidity for an entire home. It requires installation by a professional because it’s connected to the ductwork that’s already installed for central air and heating purposes.
  • Heat pump humidifier—This works similar to a refrigerator-style dehumidifier. These are whole-house units that use a fan to pull the moist air into the system and across a cold coil. The condensed water drops into a water collection tank that is then drained through a hose. The air is warmed again prior to being blown back through the exhaust and into the home.
  • Pump dehumidifier—This type of unit uses a pump to move the water out and doesn’t rely on gravity for the water to flow from the unit.
  • Chemical absorbent dehumidifier—Working similar to a desiccant dehumidifier, this system uses a heat exchange wheel with a desiccant chemical to absorb water vapor in the air.
  • Dehumidifying ventilator—This ventilator uses a sensor and an exhaust fan to remove moisture from the air. The sensor controller takes in the ambient humidity level and activates the unit to turn on the ventilator to remove any humidity.
  • Homemade dehumidifier—For those who want to make their own dehumidifier, combine rock salt, calcium chloride, silica gel, or another readily available absorbent. Typically, these moisture absorbing substances are put in a bowl and placed in a room to draw moisture from the air.

Anatomy of a dehumidifier

Before getting into how a dehumidifier works, here’s a breakdown of its main components:

  • Air filter—Located behind the grill in the dehumidifier case, the air filter traps dust and debris so it doesn’t contaminate the evaporator fins and condenser coils.
  • Collection bucket—This container is positioned under the evaporator to collect the condensation from the evaporator.
  • Control board—The control board displays the selection buttons and indicators to properly control the dehumidifier functions.
  • Compressor—This is a pump that compresses the refrigerant gas that runs through the evaporator to initiate the cooling process and water extraction. 
  • Evaporator—This is a heat exchanger that cools air and condenses water to dehumidify the room.
  • Fan—The fan blows air across the evaporator and condenser heat exchangers to aid in cooling and dehumidification.
  • Humidistat—This sensor detects the amount of water vapor or humidity percentage in a room. 

How does a dehumidifier work

Dehumidifiers work in one of two ways—by refrigeration or by absorption/adsorption.

Refrigeration

  1. Air is drawn through an electric fan grill on the side of the unit.
  2. The warm air passes over freezing cold coils that are filled with a coolant.
  3. As the air cools, the moisture condenses and drips downward off the coils and into a collection tank. 
  4. The air passes over a heating element and warms back up to its original temperature.
  5. Warm, dry air is blown back into the room. 
  6. As the collection tank fills, a plastic float in the machine rises. 
  7. When the tray is full, the float trips an electric switch that turns off the fan. This switches on an indicator light telling telling you to empty the tank.

Absorption/adsorption

  1. A blower forces air into the unit.
  2. The air passes over a rotating desiccant wheel. 
  3. The desiccant absorbs the amount of moisture in the air and releases about 75% of the air back into the space as dry air.
  4. The other 25% of air is heated up to over 200 degrees Fahrenheit. The high temperatures drive the moisture out of the desiccant material.
  5. This warm, wet air is then released through ductwork outside the unit (usually outside the home or office).

Alternatives to a dehumidifier

If you have a smaller space and don’t have enough room for a dehumidifier, try these alternatives to remove moisture from your air:

  • Put silica gel or other desiccants in a bowl.
  • Run a fan in the room.
  • Run your air conditioner.
  • Use a wood stove or space heater.

Maximizing the efficiency of your dehumidifier

Running a dehumidifier will make the air in your home more comfortable, but you don’t need to run it 24/7. Here are some tips for maximizing the efficiency of your unit:

  • Turn off the dehumidifier once humidity drops to an acceptable level. Dehumidifiers are most effective at removing moisture when humidity levels are higher than 50%. 
  • Only run the unit as needed. For example, humidity levels in the winter are generally low, so you don’t need to run your dehumidifier as much during this season. 
  • Clean dehumidifier coils annually.
  • Keep windows and doors closed during use.
  • Empty the collection tank frequently or when the empty tank light comes on.
  • Reuse the greywater in the collection tank to water plants.

Reasons why a dehumidifier makes sense

Too much moisture indoors can lead to several health issues and cause damage in your home. Dehumidifiers help to:

  • Prevent the growth of mold and mildew
  • Eliminate musty odors
  • Reduce “sweating” on cold water pipes
  • Keep electronics and optics in good working condition (moisture can lead to rusting or short circuits)
  • Maintain a comfortable environment
  • Relieve allergies and sinus issues
  • Protect the wood in your home

How to choose the right dehumidifier for you

The best dehumidifier for you will mainly depend on the size of the space you want to put the unit in. A dehumidifier’s size is determined by its total capacity to remove moisture. The capacity is rated in pints of moisture removed per day (within a 24-hour period.) Its capacity indicates how large of a space it will cover in square feet.

You’ll need to know the square footage of the area you’d like to dehumidify to get an idea of the capacity you’ll need.

Other factors such as style, custom humidity settings, digital displays, and more are based on personal preference and budget.

Best dehumidifiers

Here are our top recommendations for dehumidifiers:

Pros
Cons

Frigidaire Energy Star Dehumidifier

Pros

Modern style, custom timer and humidity settings, removes up to 70 pints of moisture in a 24-hour period

Cons

No drain pump for continual draining, heavy and not super portable

Keystone Energy Star Dehumidifier

Pros

Durable wheels, digital display, quiet, 1-year manufacturer's warranty

Cons

Mold can grow in the reservoir if not routinely cleaned

LUOYIMAN Electric Home Dehumidifier

Pros

UV light removes formaldehyde, bacteria, dust, and mold, it comes with LED indicators, it features a sleek design, and it has a safe auto shut off

Cons

Fills slowly, can overheat

Frequently asked questions

What should my ideal indoor humidity level be?

The ideal indoor humidity levels for health and comfort is about 40–50%.

How much electricity does a dehumidifier use?

A dehumidifier uses about 4.2 cents of power per hour. Energy efficient rated units will use less.

How much noise does a dehumidifier make?

The noise level will depend on the brand. Some units are as subtle as a house fan.

How often do I need to empty my dehumidifier?

Empty the collection tank whenever it’s full. Depending on the humidity levels in your home, you may need to empty your bucket once every two days to twice a day.

Can I run a dehumidifier with my air conditioner?

Run a dehumidifier only if your space has excess relative humidity. Typically, your air conditioner will do a good job of removing excess moisture from the air in your home.

Will a dehumidifier make my room hotter?

Dehumidifiers generate heat to operate. Removing humidity from the air will cause the dehumidifier and your room to heat up.

What’s the difference between a single-room dehumidifier vs. a whole-home dehumidifier?

Single-room dehumidifiers are designed to remove air moisture from one room. Whole-home units are large or fixed appliances that will remove moisture from larger spaces.

Does a dehumidifier kill mold?

Dehumidifiers don’t kill mold, but they do prevent it by reducing the humidity levels inside your home.

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