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How does a dehumidifier work?

These units keep your home comfortable and safe

How does a dehumidifier work? Credit: Reviewed / David Ellerby

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Rising summer temperatures make for high humidity levels as warm air holds more water vapor. Humidity doesn’t just make you feel sticky; it can affect air quality and damage your home.

Dehumidifiers aren’t just for summer, though! Damp basements, crawl spaces and closets are a year-round problem, and you may be wondering how does a dehumidifier work.

A dehumidifier removes moisture from the air. Let’s face it, though, you probably don’t care how a dehumidifier works, as long as it makes your indoor air more comfortable.

That said, more info will help you get the most from your dehumidifier, choose the right type, keep its running costs down, and even help it last longer.

How does a dehumidifier work?

There are three types of dehumidifiers: Refrigerating, desiccant, and thermo-electric. All of them remove moisture from indoor air. Which type is best depends on where and how you’ll be using the dehumidifier.

Dehumidifier types: Which one is right for you?

1. Refrigerating dehumidifiers

  • Pros: Removes a lot of moisture from the air | Good for large spaces
  • Cons: Noisy compressors | Work best in warmer spaces

Like your refrigerator or air conditioning unit, refrigerating dehumidifiers contain compressors that cool a heat exchanger and remove heat from the air.

Air cooling is at the heart of the dehumidifying process because the cooler air gets, the less moisture it can hold.

Refrigerating dehumidifiers use a fan to pull air across a cold heat exchanger. When warm, humid room air hits the cold heat exchanger, excess moisture condenses as water. This drops down into a collection reservoir.

The heat removed from the air doesn’t just disappear. Some of it is recycled to rewarm the air before it returns to the room. The only difference between dehumidifiers and air conditioners is that the AC dumps the heat outside and returns the cool air to your home.

To keep the dehumidifier running, you need to get rid of the water it collects.

Most refrigerating dehumidifiers have a drain hose attachment as well as a collecting reservoir. If you have a drain below the level of the dehumidifier, you can let the water trickle down the tube and drain away.

Dehumidifier floor drain
Credit: Reviewed / David Ellerby

Dehumidifier emptying is easy if you have a floor drain.


Unfortunately, most homes don’t have floor drains. This means you could be carrying a lot of water.

If you’re going with manual emptying, choose a dehumidifier with a good reservoir handle and easy emptying. Our Energy Star rated favorite for manual emptying is the LG Puricare 50 Pint (UG501KOG5).

Credit: Reviewed / David Ellerby

Dehumidifer buckets can be emptied by hand, but are a heavy lift.


To reduce manual emptying, consider a dehumidifier with a pump. This costs more than a basic model. The extra investment is worth it if you’ll be using the dehumidifier for long periods or you might have difficulty carrying and emptying the reservoir.

$329 at Amazon

2. Desiccant dehumidifiers

Desiccant dehumidifier
Credit: Reviewed / David Ellerby

A desiccant dehumidifier, ideal for removing damp from small spaces.

  • Pros: Don’t need power | Small and inexpensive | Some have a reusable desiccant
  • Cons: Best for small spaces | Need regular recharging or replacement

You know those small packets labeled “silica gel desiccant, do not eat”? A desiccant dehumidifier is a much larger version of one of these. A desiccant is any substance that’s particularly good at absorbing water. Silica gel and activated carbon are the most commonly used because they’re effective and safe.

The very simplest versions of these dehumidifiers are vented boxes full of desiccant. They don’t use any power, and if placed in humid air, they’ll gradually absorb water.

One of the best desiccant dehumidifiers, the Eva-Dry E-500, has the added advantage of reusable desiccant with a color indicator. The desiccant changes color when it needs drying out, and plugging it into an outlet dries it out to make it as good as new.

There are a number of disposable options, like a two-pack of DampRid Moisture Absorbers. Once opened to expose the desiccant, they’ll go to work, and when the desiccant is full, you throw them away.

$25 at Walmart$25 at Amazon

3. Thermo-electric dehumidifiers

  • Pros: Quiet | Energy efficient
  • Cons: Limited to small spaces

These are sometimes called Peltier dehumidifiers. Most manufacturers simply market them as small or mini dehumidifiers without mentioning how they work.

If a dehumidifier uses electricity, looks like a mini version of a refrigerating dehumidifier, and doesn’t have a compressor, it’s probably a thermo-electric dehumidifier.

They work like a refrigerating dehumidifier, cooling the air to condense out the humidity and collect it in a reservoir.

Instead of a compressor, they pass electricity through two different materials, cooling them where they meet. This is called the Peltier effect, or thermo-electric cooling.

The advantages are no noisy compressor, like in a refrigerating dehumidifier, and apart from a fan, there aren’t any moving parts. This makes them inexpensive.

So thermo-electric dehumidifiers are quiet, simple, and cheap; there’s got to be a catch, right? Unfortunately, they can’t remove as much moisture as a refrigerating dehumidifier.

They’re best suited for small spaces like closets, RVs, and because of the low noise, small bedrooms.

What size dehumidifier do I need?

When it comes to the question, "How does a dehumidifier work?" choosing the right size for your space is crucial to achieving optimal performance. For a closet, small bedroom, or bathroom, consider a desiccant or small thermo-electric dehumidifier.

For larger rooms, you’ll need a refrigerating dehumidifier. They’re rated by the amount of water they can remove in 24 hours. There are guidelines based on floor space.

Generally, it’s better to go for the high end of the recommended size range. A smaller dehumidifier could run constantly and burn a lot of energy if it’s struggling with the humidity in too large a space. If your dehumidifier runs less often, it will also decrease noise levels.

The extra capacity could also help cope with seasonal peaks in humidity or drying out after emergencies like leaks or spills.

How to care for your dehumidifier

Airflow is essential, so place the dehumidifier as centrally as possible in your space.

For refrigerating dehumidifiers, keep the filter and heat exchanger clean. Remove the filter and vacuum it (some are also washable), and gently run a vacuum nozzle over the heat exchanger. If these get clogged with dust, the dehumidifier will use more energy.

Filter cleaning
Credit: Reviewed / David Ellerby

Clean filters for good airflow keep a dehumidifier running smoothly.


For dehumidifiers with a collecting reservoir, remember to empty them regularly, and keep them clean by washing them with dish detergent.

Desiccant dehumidifiers need regular checks to make sure the desiccant is still working. Follow the manufacturer’s instructions to recharge or dispose of and replace the desiccant.

When should I use a dehumidifier?

For really high humidities, your body is your best guide. Your skin will feel clammy, and it’ll be obvious you have a humidity problem.

This happens when the relative humidity, indicating the amount of water vapor in the air, hits about 70%. Comfort isn’t your only concern. Once the relative humidity goes above 60%, this encourages mold growth and dust mites.

If humidity above 60% is potentially bad, why not just get the air as dry as possible?

Unfortunately, low humidity dries out your skin, irritates your eyes, nose, and throat, and makes you more vulnerable to respiratory infections and asthma symptoms.

Dry air is also bad for your home. For example, wood flooring can crack when the humidity is too low.

Aiming for 50% relative humidity, or at least a range from 30% to 60%, is the best compromise. This minimizes the risks of excessively high or low humidity. That’s a pretty narrow target, and it’s important to know if you’re hitting it.

If you want to be certain, it’s worth investing in a [humidity meter]. This can be a basic model like the like the ThermoPro Digital Hygrometer Indoor Thermometer showing current conditions or something more sophisticated like the SensorPush HT1 Wireless Thermometer/Hygrometer to record of how conditions change over time.
$10 at Amazon$50 at Amazon

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