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How a dehumidifier works

Too much moisture in the air can quickly make your home uncomfortable. It can lead to health problems, too.

High levels of water vapor in the air, known as humidity, are common during hotter months because warm air can hold more moisture than cold air. While location and season influence humidity, a home’s layout and construction also may create spaces where humidity is high.

To lower humidity and make spaces more comfortable and safe, you need a suitable dehumidifier.

How humidity works

The amount of water vapor in the air at any given moment is referred to as humidity. When the air is dry, humidity is low, and when the air feels wet and heavy, the humidity level is high. Too much or too little humidity leads to discomfort and health concerns.

In cold, dry winter months, a lack of humidity can cause itchy, cracked skin and breathing problems. Too much humidity, however, can exacerbate asthma or allergies and create an atmosphere suited for harmful organisms, including mold and mites. Some people may have trouble sleeping in both situations.

When most people discuss humidity, they are referring to relative humidity, which is the measure of moisture in the air compared to how much the air can actually hold. This measurement is expressed as a percentage.

Best humidifier

While everyone has preferences, most people desire a relative humidity of 35% to 50% throughout the year. To add moisture to the air, you need a humidifier; to remove the water vapor and lower relative humidity, you need a dehumidifier.

Where humidity comes from

Water vapor comes from a variety of sources within and without the house. The simple act of breathing adds water to the air. However, inside an enclosed space, appliances such as dishwashers and dryers expel warm air and moisture. Hot showers, tea kettles and even fish tanks are contributors to humidity too. 

When paired with seasonal high temperatures, these devices and activities exacerbate relative humidity.

How to measure humidity

Best hygrometer

Humidity is measured by a hygrometer. They’re handy to have, particularly if you’re concerned about water vapor in the air and its consequences. Some weather stations measure relative humidity and other key metrics from outside your home.

However, you don’t need such devices to determine if you need a dehumidifier. Sometimes the weather or season will dictate that. You also may be able to tell the air is too moist by how it feels on your skin, or if you notice condensation in certain spaces.

How dehumidifiers work

A dehumidifier draws in warm air from the immediate area, bringing it in contact with cool coils within the machine. When they make contact, condensation forms and is collected.

Dehumidifier pros

By removing moisture from the air, a dehumidifier provides short- and long-term comfort and health benefits.

  • Dehumidifiers prevent the growth and spread of mold and mildew.
  • Insects such as silverfish and cockroaches are attracted to warm spaces, particularly where there is mold. A dehumidifier can help prevent their spread.
  • While dehumidifiers don’t cool the air, dry air is more comfortable.
  • Too much humidity may exacerbate breathing conditions such as asthma. A dehumidifier eases these.
  • Dehumidifiers may reduce allergens causing itchiness, sneezing or chest pain.

Dehumidifier cons

It’s harder to remove moisture from the air than it is to add it. While most humidifiers are small, quiet and inexpensive, the most powerful dehumidifiers are bulky, noisy and pricey.

How much a dehumidifier can cover

Dehumidifiers have a limited range from which they can draw moisture. Some are designed for small bedrooms while others are suited for large common areas. Consider what room or rooms need attention and how best to use your resources. Some spaces, particularly basements, may require a regularly running machine, while others may only temporarily need a dehumidifier.


A dehumidifier removes water from the air and places it into a reservoir, which needs to be emptied regularly. Note the size of the reservoir, which indicates how much water it can hold, as well as the machine’s power, which informs the rate at which it fills up.

While smaller dehumidifiers may remove 1 liter or less of water from the air a day, the biggest ones extract up to 30.


Basements, especially if they house washers and dryers, and bathrooms where you enjoy a hot shower or bath are two spaces most often in need of a dehumidifier. Attics — or any room with poor ventilation or a lack of air conditioning — also may require a dehumidifier.

How to use a dehumidifier

There are some precautions to take before and while using dehumidifiers, as well as useful features to enjoy.

  • Clean the space before use, paying special attention to dust and dirt. The machine can spread around particles, which can also clog the filter.
  • Position the dehumidifier at least a foot from any walls or flat surfaces so as not to block inflow or outflow.
  • Close windows and doors so air doesn’t continually circulate and bring in more moisture.
  • A humidistat identifies the current relative humidity in the space. On most dehumidifiers, you can set your desired humidity.
  • Programmable dehumidifiers let you set a specific time to run, such as during the day when you are out, or overnight to conserve energy.
  • Continuous drainage lets a hose expel water into a nearby sink or drain so you don’t need to empty a container.
  • Clean the air filter at least once a month.


Compact dehumidifiers for bathroom or bedroom use cost $30-$60. To cover the average common space or living room, however, expect to pay from $150-$250.

Best dehumidifiers

Best Frigidaire 22-Pint Dehumidifier

Frigidaire 22-Pint Dehumidifier

This mid-size dehumidifier comes from a trusted name and offers plenty of value for most spaces. It features an automatic shut-off and a rear spigot for continuous drainage, as well as caster wheels for easy movement.

Where to buy: Sold by Amazon

Best Pro Breeze Mini Humidifier

Pro Breeze Mini Humidifier

For smaller spaces, this compact, quiet dehumidifier creates a comfortable atmosphere with easy operation. An automatic shut-off and full water tank light provide convenience. 

Where to buy: Sold by Amazon

Best Black and Decker 1,500-Square-Foot Dehumidifier

Black and Decker 1,500-Square-Foot Dehumidifier

This Energy Star-certified dehumidifier is good for medium to large spaces such as basements. It’s portable and removes up to 20 pints a day.

Where to buy: Sold by Amazon


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Anthony Marcusa writes for BestReviews. BestReviews has helped millions of consumers simplify their purchasing decisions, saving them time and money.

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