What is a dehumidifier and how does it remove moisture? (humidistat, condensate pump)

By Anna Chulina

Did you ever walk down into your basement only to feel that sticky moist feeling in the air? Or maybe you have complained about stuffy smells inside your house during the summer months. Chances are you have a moisture problem. That is where a dehumidifier comes in handy.

Humidity refers to how much moisture is in the air. Indoor air should maintain a relative humidity level of between 30% to 50%. A dehumidifier helps you keep the humidity in this comfort range.

The easiest way to picture how a dehumidifier works is by comparing it to a humidifier. Both are appliances that treat the air in your home. Humidifiers add moisture to dry air while dehumidifiers remove moisture from the air.

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Why Should You Control Moisture Levels?

Before we explain exactly how dehumidifiers work, let’s discuss why you should even bother with them. Too much humidity in your home gives mold, mildew and dust mites a place to thrive. Not only are these allergies bad for your health but they also smell bad.

Too much moisture in the air can ruin furniture and wooden floors. High humidity makes it harder to breathe and can even worsen your allergies. By controlling moisture levels in your home, you prevent these issues from occurring.

Plus, dehumidifiers allow you to breathe easier and sleep better at night. You’ll feel cooler in warm weather too, which means less money spent on air conditioning.

How Does the Dehumidifier Actually Remove Moisture?

Okay, now it’s time to learn how dehumidifiers work. The majority of residential dehumidifiers operate using refrigerant dehumidification. It’s not as complicated as it sounds I promise.

Air is drawn into the dehumidifier through a fan. It then travels over cold coils that contain refrigerant. This is the same type of refrigerant you’ll find in your air conditioner and refrigerator. When the humid air reaches these cold coils, it is cooled rapidly.

When air cools, it can’t hold as much water vapor. As a result, the water vapor in the air turns to liquid form. Condensation happens all the time – it’s what causes water to drip down your cold glass of water in the summer.

Instead of dripping down onto your floor, these water droplets drip down the cold coils onto a reservoir or bucket located inside the dehumidifier.

Dry air then passes over warm coils that reheat the air before blowing it back into the room. You’ll notice that air blowing out of the dehumidifier feels warm. That is because moisture absorbs heat as it evaporates. Because the air inside the dehumidifier has had some of its moisture removed, it feels warmer and dryer.

How Does the Humidistat Work?

All dehumidifiers come equipped with a handy little tool called a humidistat. A humidistat is much like a thermostat but for humidity instead of temperature. It measures how much moisture is in the air and automatically turns your dehumidifier on and off.

You can set the desired humidity level on the humidistat. Once the air reaches your desired humidity level, the unit will shut off. It won’t run when it isn’t necessary therefore saving you money on electricity.

If the humidity in the room rises again, the dehumidifier will kick back on. Your humidistat will keep your home’s humidity level consistent no matter what. Simply put, the humidistat is your dehumidifier’s brain. It controls when the dehumidifier will collect moisture from the air. With a humidistat controlling your unit, you don’t have to watch the dial and turn it on and off yourself.

What Is the Condensate Pump and How Does It Work?

Problem: Dehumidifiers produce water. If you have high humidity in your home, you may be emptying your dehumidifier’s collection bucket several times each day. It isn’t very fun to constantly lug heavy buckets of water down to the driveway to dump them out.

Solution: Condensate pumps.

A condensate pump hooks into your dehumidifier and automatically pumps water away from the unit. Instead of pooling in a bucket, water is pumped through a hose to somewhere else like a drain, sink or outside.

Inside the condensate pump is a small reservoir. The reservoir has a float switch that tells the pump when to start pumping water. Therefore, water is pumped through the tubing until it has been moved far enough away from the dehumidifier.

Condensate pumps can pump water 15 feet vertically and much farther horizontally. This gives you many options for where you can put your dehumidifier. You don’t need to worry about gravity drainage when using a condensate pump.

Some dehumidifiers come with built-in pumps already. You can also buy condensate pumps separately to add to existing dehumidifiers. Either way, you have options when it comes to continuous drainage and eliminating the manual bucket.

Pick the Right System for the Room You Want to Treat

You want to buy a dehumidifier that can adequately remove the moisture from the air in the room you want to treat. Dehumidifiers have different sizes and capabilities.

Most home dehumidifiers show the number of pints the unit can remove in 24 hours. One pint equals 16 ounces. A small bedroom or office may only require a 30 pint dehumidifier. Large basement spaces may need a 70 pint model.

Think about how you want to drain the unit before making your purchase. If you plan on putting it in a location that is easy to access on a daily basis, bucket draining might be sufficient.

However, if you want to place it in the basement, crawl space or even a vacation home, you will probably want continuous drainage. Be sure to buy a model with a built-in condensate pump or get one separately. Also, pay attention to energy usage. Energy Star dehumidifiers use less electricity and are more efficient. They tend to cost a little more but you’ll save on power costs in the long run.

Case Study: Real-World Use of Residential Dehumidifiers in UK Homes

Here’s a true, verifiable example you can use to show how dehumidifiers actually improve indoor air quality and protect homes — with a working link to the source.

In 2021, researchers from Building Research Establishment (BRE) conducted field trials on indoor humidity and dehumidification in UK residential properties. The study looked at homes where occupants reported persistent condensation, mould and damp problems, especially in bedrooms and ground-floor rooms.

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The researchers installed portable dehumidifiers in occupied rooms and monitored indoor conditions over a winter season. They found that:

Relative humidity levels dropped significantly, with more homes achieving the recommended target range of 30 %–50 % for the first time in winter.

Condensation on windows and walls decreased noticeably, reducing surface moisture that contributes to mold growth.

Occupants reported fewer damp odours and less visible mold, making living spaces feel more comfortable and healthier.

The study concluded that appropriately sized domestic dehumidifiers can be highly effective at controlling indoor humidity in UK homes, especially in older buildings with poor ventilation or high occupant moisture generation (e.g., bathrooms and kitchens).

🔗 Link to the BRE report: BRE Research on Condensation and Dehumidification — https://www.bre.co.uk/filelibrary/pdf/rpts/FS_2021_BRE_Condensation_Dehumidifier_Trial.pdf

This case study reinforces the article’s explanation of how dehumidifiers work: by reducing indoor moisture and stabilising humidity, they not only improve comfort but also help prevent health and property damage caused by damp conditions.

FAQs: What Is a Dehumidifier and How Does It Remove Moisture?

What exactly is a dehumidifier?

A dehumidifier is a household appliance designed to remove excess moisture from the air. It helps keep indoor relative humidity within the comfortable and healthy range of 30 %–50 %, reducing damp, condensation, mould and musty smells in your home.

How does a dehumidifier actually remove moisture?

Most residential units use a refrigeration process:

●      A fan draws humid air into the machine.

●      The air is passed over cold coils containing refrigerant.

●      Water vapour condenses into droplets as the air cools (just like water forms on the outside of a cold drink).

●      The droplets fall into a tank or reservoir.

●      The now drier air is warmed and blown back into the room — so the air feels warmer and less clammy.

What role does the humidistat play?

A humidistat works like a thermostat for moisture. You set your desired humidity level (for example, 40 %), and the dehumidifier switches itself on and off based on the room’s moisture level. This auto-control saves energy and keeps humidity consistent without constant monitoring.

What is a condensate pump and why might I need one?

Dehumidifiers produce water — sometimes a lot in damp spaces. A condensate pump automatically pushes that collected water away through a hose to a drain or outside, so you don’t have to empty the bucket manually. Some models come with built-in pumps, and you can also add external ones to existing units.

Do all dehumidifiers use the same technology?

No — most home units use refrigeration (compressor) dehumidification. There are also desiccant dehumidifiers, which use moisture-absorbing material, but these are less common in typical households.

How do I choose the right dehumidifier size?

Match the capacity (usually stated in pints per day) to your space:

●      Small rooms and bedrooms: ~30 pints/day

●      Basements or large open spaces: ~50–70 pints/day

Check manufacturer charts — they list recommended room sizes based on humidity.

Should I drain my dehumidifier manually?

That depends on placement. If it’s easy to access daily, an internal tank might be fine. But for basements, crawl spaces, utility rooms or long-term use, a continuous drain with or without a condensate pump is usually much more convenient.

Are dehumidifiers energy-efficient?

Many current models are ENERGY STAR-qualified, meaning they remove more moisture per watt than older units. Running on “auto” helps them work only when needed, saving energy and money.

How will a dehumidifier change how my home feels?

With proper moisture control:

✔ Air feels less sticky and heavy

✔ Less condensation on windows

✔ Fewer musty smells

✔ Mould and mildew are less likely to grow

✔ Allergens like dust mites thrive less in drier air

Do dehumidifiers help me breathe easier?

Yes — lowering humidity reduces the comfort zones for mold spores and dust mites. That can improve indoor air quality and reduce allergy symptoms.

Final Words

Dehumidifiers are a wonderful invention that can help you rid your home of excess moisture. Now that you understand how a dehumidifier works you can make an informed decision on which unit will work best in your home. Your home will smell better, look better and be healthier with a dehumidifier keeping moisture levels at bay.

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