How Does a Dehumidifier Work In a Basement?


Dehumidifiers can be a clunky, unattractive kind of appliance, so I completely understand why so many homeowners are hesitant to buy one.

But in dark and damp places like basements where the dehumidifier is out of sight, a dehumidifier is an absolute must.

But how do dehumidifiers work in basements? They work like any other dehumidifier in that they take in the ambient air, cool it off to condense and collect water, and then blow the processed air back into the room. There are few special considerations when it comes to basements, however. The ideal dehumidifier must have a high capacity for automatic water removal, as well as be able to handle cold temperatures without breaking down.

It can be easy to pick the wrong dehumidifier, only to throw it away in a year or two.

So let’s take a look at what’s important so that this doesn’t happen to you.


How Dehumidifiers Work

A dehumidifier can be thought of as having two parts.

First, air is drawn into the unit by fan. The air is then run across cold coils, allowing it too cool down into water condensate. This water condensate is then collected into a container that must either be emptied manually or is continuously emptied out by a water hose.

Second, a heating element warms up the processed condensate, blowing it back into the room again. This description is what we’d call a typical portable dehumidifier, or refrigerant dehumidifier.

There are of course other ways to dehumidify such as a desiccant dehumidifier or a whole house dehumidifier that’s attached to the HVAC, but most people think of portable units that run air through coils by using a built-in heat pump when talking about dehumidifiers in general.

Why Dehumidifiers Are Especially Important In a Basement

The interior of a home must maintain a humidity level between 30% and 50%. This is the EPA’s recommendation, but to me, it’s a must.

You shouldn’t go below 30%. Our bodies are made up of water and naturally need at least 30% humidity levels in their environment for the body to function. This low level would be hard to achieve anyway, so it usually isn’t a problem in most homes.

It’s once we get above 50% RH where the trouble starts. This is when mold starts to form to create the unhealthy environment known as the musty basement full of odors. All sorts of microscopic things grow in this environment like bacteria and viruses, not just mold.

If you think this isn’t a problem since you rarely spend any time in the basement, think again. Any impurities in the basement’s air will naturally move up to the higher levels of the home, causing respiratory problems and discomfort. When dust combines with high humidity, it causes asthma and allergies to flare up.

High moisture also damages the building materials of the home and can end up quite costly in the long run.

Not stopping the humidity problem early in its tracks turn something as simple as cleaning an area with bleach over a few weekends and then bringing it back to normal by getting a dehumidifier into a costly mold remediation process costing thousands of dollars.

If your basement humidity is severe, you’ll need more than just a dehumidifier. Here’s a post that can help – use it as a resource to put together a plan on how to fix a serious basement problem.


What Size Should Your Basement Dehumidifier Be?

Just like an air purifier or any other appliance that’s based on taking in air through a fan and cycling it continuously, a dehumidifier also has to be big enough for the space.


The Four Types of Basement Humidity Conditions

Since there is so much misinformation out there when it comes to dehumidifiers, it’s refreshing that the Association of Home Appliance Manufacturers (AHAM) and Energy Star have put an effort into helping us categorize a room by how damp it feels.

Here’s how much water your dehumidifier should be removing per 24-hour period (in pints) based on the dampness level and square footage (sourced from AHAM’s guidelines):


Condition #1: Moderately Damp

A musty odor appears, but this condition is typically due to outside weather being humid.

Area (Sq. Feet)5001,0001,5002,0002,500


Condition #2: Very Damp

A step up in severity, here the indoor dampness starts persisting (despite weather) and spots start appearing on the walls on corners of base molding and floor.

Area (Sq. Feet)5001,0001,5002,0002,500


Condition #3: Wet

This is when water starts accumulating or leaking slowly, but isn’t described as large pools of water or flooding.

Area (Sq. Feet)5001,0001,5002,0002,500


Condition #3: Extremely Wet

The worst condition possible short of flooding. Here, sizeable pools are starting to form.

Area (Sq. Feet)5001,0001,5002,0002,500


So for someone who has half a basement under their home (about 500 to 1,000 square feet), the dehumidifier should be able to remove somewhere between 10 to 14 pints of water per day if moderately wet, but may need to remove as many as 23 pints per day if the basement falls in the extremely wet category.

Are these tables perfect?

Of course not, but it’s a good starting point. You see, there’s just one problem –

This information doesn’t talk about temperature.


How Incorrect Temperatures Make You Pick the Wrong Dehumidifier

The higher the temperature in a basement, the easier it will be to extract the water. If you pay attention to any dehumidifier’s user manual, you’ll notice that most can only operate above a certain temperature.

Mostly, this temperature will be 65 °F. If you live in the Northern US or Canada, this will seem like a joke.

Basements are cold and damp anyway, so this essentially means that they’ll only work in the summer for many consumers.

Operating this kind of dehumidifier the moment the season gets colder will cause its coils to freeze over. The dehumidifier then constantly keeps running and your electricity bill skyrockets. Finally, you stop the madness and throw it out, claiming that it didn’t work and was a waste of money.

Sadly, manufacturers advertise their dehumidifiers’ capacities at temperatures set by laboratory tests, which are either 80 or 86 °F, so many consumers with cold basements end up wondering why their dehumidifier didn’t work as described.

The solution then is to find a way to buy a dehumidifier that will last as long as possible.

How to Ensure Your Dehumidifier Lasts For Years

Go Up In Size

Don’t force your dehumidifier to do more work than it’s capable of doing.

If after doing your research you’ve finalized your choices between a 15-pint or 18-pint dehumidifier, buy the one that’s 18 pints. The dehumidifier won’t be overworked and will last longer.


Get Ahead of Winter

The Department of Energy (DOE) recommend that a dehumidifier be used the most in the summer, with casual use in the spring and fall. According to them, a dehumidifier doesn’t need to be on during the winter.

Obviously, everyone’s situation is different. You know the climate of your region best. Run your dehumidifier as much as possible right before the cold season starts, clean out the basement, seal any cracks in the slab, foundation walls, and cover up the sump pump.

By getting the house in order so to speak and getting your humidity levels in check right before winter, you should be more comfortable packing up the dehumidifier and waiting for the winter to be over to turn it on again.

This way, you won’t have to worry about your dehumidifier’s coils freezing over and it will last you another year.


Consider a Desiccant Dehumidifier or One That Can Operate At Lower Temperatures

Although most dehumidifiers won’t work below freezing temperatures, there are some that will operate below 65 °F. You won’t have to worry about frozen coils with desiccant dehumidifiers, so this might be a good option.

I like the Ecoseb 21-pint desiccant dehumidifier. The 21-pint capacity is a good size for most average basements out there.

Contrary to the popular belief that a desiccant dehumidifier can only work in small rooms, desiccant dehumidifiers are now being manufactured for larger spaces and are perfectly fine for basements if you find the right one.

Other Considerations

For convenience, a dehumidifier with as many automatic features as possible is ideal.

That means one that turns itself on and off automatically if there is an issue with the water collection that could potentially flood the home. It means one with an auto defrost function for the coils. It also means one that has an attached hose that automatically drains to the exterior of the home, commonly known as continuous drainage.

Beyond that, you have to look at your basement as a whole.

If you have mold issues, a dehumidifier alone isn’t enough. Dead mold spores are still present and release toxins; those that are alive will continue multiplying.

In other words, a dehumidifier should be seen more as a preventative measure. While using it in a mold-infested basement may help to some degree, you still need to take care of the underlying issue.

This may mean persistently cleaning the walls and surfaces from mold on a weekly basis until the mold doesn’t come back. Also, consider combining a dehumidifier with a powerful air purifier.

Many air purifiers have ozone-free features that kill microbes. An air purifier with a heavy activated carbon filter can also trap some of the toxins that mold spores release into the air, while an air purifier with a HEPA filter can help you trap the actual mold spores.

Just make sure to change out the filters constantly. Otherwise, it won’t work. You can get all those features combined in one air purifier if you look for them. I personally use the Winix air purifier with its PlasmaWave technology and have never had any health issues.


Related Questions

Where in the basement should I place my dehumidifier?

It’s best to place it somewhere in the center. That way, you can keep the interior doors open so that as much of the air is cycled as possible. A dehumidifier should be kept away from walls, as well as patio doors and windows. It should also be kept away from messy workstations in the basement that may cause damage to it (like a woodworking station).


What if I still want to run the dehumidifier in the winter but my basement is freezing cold?

Consider using a heater and dehumidifier in the space. That way, the basement temperature can be brought up above the operating temperature of the dehumidifier. Keep in mind, however, that humidity also tends to be lower at low temperatures. Measure the humidity first with a hygrometer to determine if this solution really is necessary.

Next, check out our dehumidifier buyer’s guide for each room in your home.