What Is the Difference Between Air Purifiers and Dehumidifiers?


On the surface, it may seem that air purifiers and dehumidifiers are vastly different. One takes out pollutants from the indoor, the other moisture.

But besides this seemingly obvious fact, there are a lot more interesting differences between these two devices.


So What Is the Difference Between Air Purifiers and Dehumidifiers?

Their main difference comes from what they can do. An air purifier is an overall solution to clean the air inside a home, while a dehumidifier helps control excess moisture. Ideally, both appliances should be used together to improve the quality of air inside a home.

The Technology Behind Each

Air Purifiers

Air purifiers typically have a succession of several filters, with each filter being able to trap certain kinds of pollutants found inside the air of a home. The first filter is usually a pre-filter. This is a basic filter that traps the larger particles like pollen, pet dander, or dust.

Next is the core filter. Depending on its capability, this filter will filter out many of the pollutants that affect indoor air quality. These may be smaller pieces of pollen, pet dander, and dust, but can also include some fine particles, depending on the filter.

For example, a True HEPA (high-efficiency particulate air) filter may remove particles as small as 0.3 micrometers in size, while some other HEPA-like filters may only be able to trap particles that are 2.0 micrometers in size. If you’d like to learn more about the particle sizes of indoor air pollutants, read this blog post. However, the range between 0.3 and 2.0 micrometers in size typically includes many small pollutants like smoke and bacteria. It may include mold spores, but those are 3 micrometers in size or larger typically.

A good air purifier often has an activated carbon filter, and this is often the next filter after the core filter. This step in the process allows smaller pollutants to be caught that passed through the first two filters. It mostly includes volatile organic compounds (VOCs), which are typically pollutants that your furniture, building materials, walls, paints, and cleaning supplies give off inside the home. Activated carbon filters also trap tobacco smoke, smog, and most other pollutants that remain.

Some pollutants will always remain. An air purifier is not 100% effective at removing air pollutants (but a good one can get very close to removing 100% of them). Companies have introduced additional steps to remove those remaining pollutants, so you may see features like ionizers or UV light also on an air purifier.



Even though the functionality of dehumidifiers is vastly different from air purifiers, you may see similar features that both of them share. But first, let’s talk about what makes a dehumidifier unique.

The obvious use of a dehumidifier is to remove moisture from the air. It cycles the air in your home just like an air purifier does, but it allows the water vapor to condensate inside it.  Instead of running air through a filter like in an air purifier does, the air inside a dehumidifier runs through refrigerated coils that cool the air down. This condenses the air into water and allows the water to ultimately be collected into a container. This container can either be manually emptied out by the user, or it can be diverted to the outside of the home through a hose.

This still leaves the rest of the air inside the dehumidifier, which is cool. The air is then passed through heated coils so that it reenters the room again at the original temperature.

Dehumidifiers are rated based on the amount of water that they can remove within a 24-hour period. You might have seen dehumidifiers with a 30-pint, 40-pint, 50-pint, 70-pint, or 90-pint capacity. Higher capacities exist, but those are rarely needed for the average residential home.

While an air purifier will continue running indefinitely unless you turn it off yourself or have an automated system in place to control it, a dehumidifier will turn itself off automatically if the container is full of water. If you don’t want to worry about having to empty out a bucket of water every day, consider installing a drainage hose on your dehumidifier.

The purpose of a dehumidifier is to draw moisture from the air, not to clean the air as an air purifier does. However, some dehumidifiers can have a washable air filter inside. Although, this air filter will be nowhere near as effective as an actual air purifier is.


When to Use Each Device

Air purifiers are the go-to solution when it comes to cleaning the air in your home. At a minimum, an air purifier will be able to remove large particles from the air like pollen or dust. Most air purifiers tend to have several technologies built in like True HEPA or activated carbon filters. This means that fine particles like smoke, smog, bacteria, viruses, and volatile organic compounds (VOCs) are removed.

Air purifiers are beneficial to allergy and asthma sufferers, as they are able to remove many of the irritants in the air, like dust, pollen, second-hand smoke, bacteria, viruses, and other allergens. They’re also able to trap pollutants related to increased moisture like mold spores, but it’s only part of the solution. That’s where the dehumidifier comes in.

Dehumidifiers won’t be able to actually remove the pollutants as air purifiers do, but they can remove moisture. If you have a damp basement, you’ll definitely need to consider a dehumidifier. Basements are notorious for mold, so a dehumidifier is a great preventative measure, as well as a solution to remove already existing mold.

Are Both Appliances Portable?

Both air purifiers and dehumidifiers tend to be portable, meaning that they can be moved in between different rooms. There are exceptions, however. Some whole house air purifiers can be ducted and attached to your HVAC system. Dehumidifiers that have a built-in drainage hose will also be more difficult to move around.

An air purifier is more sensitive to how it’s positioned. To truly get the most of it, you have to calculate the capacity for its ability to move the air in the room (airflow). A dehumidifier, on the other hand, can work in corners, and it can also benefit adjacent rooms in your home just by opening the doors in between.

That’s what makes dehumidifiers so popular for basements. Not only is their ability to remove moisture a benefit, but you can easily just open all the doors in your basement rooms and dehumidify the entire space, as long as you buy a dehumidifier that has the appropriate moisture removal capacity in pints.


Do I Need an Air Purifier or Dehumidifier for Mold?

But what if you only choose one of the devices to fight mold?

It won’t be enough.

An air purifier alone will be able to trap the mold spores, but this by itself isn’t enough. First, even if you kill the mold, it will continue to give off odors while it’s sitting in the air purifier filters. And even if you change out the filter and remove the mold spores, if there is still moisture in the area, new mold will form.

If you only introduce a dehumidifier into the space, you’ll limit new mold from forming. Mold has a hard time growing in areas where the relative humidity (RH) is between 30% and 40%. As long as you can achieve this range of RH, new mold will be stalled almost immediately. But you’ll still need to remove the mold that’s still inside the room. Even dead mold spores release odors, so it’s essential to remove them. By using an air purifier, in addition to cleaning of the organic surfaces where mold deposits, you’ll be able to remove it.

So to summarize, it takes both a dehumidifier and an air purifier to remove existing mold from a room. Depending on the severity, you may even need to use additional methods to eliminate the mold.

If there is no mold yet and you’re just looking to maintain a healthy living space, then maintaining the ideal RH levels with a dehumidifier should suffice. An air purifier is still a good idea to improve the quality of the air overall.


Can a Dehumidifier Help with Pollutants?

As mentioned, a dehumidifier can help with indoor air pollution in an indirect way by removing moisture from the air. It won’t directly remove mold, but it will make it more difficult for mold to thrive once there is less moisture in the air.

Dehumidification also helps with the general “stickiness” of pollutants to surfaces. Mold spores are attracted to organic surfaces and thrive when there is moisture in the air. So, the mold is ideally looking for wood and other organic matter surfaces inside your home for nutrition. When there is more moisture in the air, it’s easier for mold to deposit on those surfaces.

You’ll find other pollutants on these surfaces as well, like dust and pollen, for example. By removing the moisture in the air, it will be more difficult for those other pollutants to deposit on those surfaces also.


Pros and Cons of Air Purifiers and Dehumidifiers


  • Both devices together can prevent pollutants like mold, dust, and pollen from sticking to the surfaces in your home. Not only does this improve your health and indoor air quality, but this also means that you won’t have to clean your home as often.
  • Dehumidifiers keep the RH in your home in check. This prevents mold and could potentially save you thousands of dollars in the future, especially if you have a basement.
  • Air purifiers with True HEPA and activated carbon filter not only filter out the large pollutants, but they also filter out fine particles like smoke, smog, mold, bacteria, viruses, and VOCs.
  • Contrary to popular belief, each appliance doesn’t require a lot of energy. As long as you buy the kind of air purifier or dehumidifier that’s the right fit for your home, each appliance uses about the same amount of energy as running a lamp or two would.



  • A dehumidifier can only remove moisture and an air purifier can only remove air pollutants. Both appliances need to be used together to fight mold and moisture.
  • Many portable dehumidifiers and air purifiers can be misused. This typically happens when the space that needs coverage is too large for the capacity of the appliance. This causes the dehumidifier or air purifier to “burn out” and to constantly be running at a much lower efficiency. This is why so many air purifiers end up not working only after a year or two. This is also where the myth that these appliances are a drain on your energy bill comes from (they’re not if you buy the right kind).
  • Each appliance requires to be on almost constantly. Turning off an air purifier any time during the day defeats its purpose and can erase all the air-cleaning it has done in the hours prior. A dehumidifier will turn itself off when it reaches the set relative humidity, but you’ll find that it too will be running during most of the day in most spaces.
  • Both appliances can be noisy since they require fans in order to circulate the air through the appliance. This typically is an issue in bedrooms for most people, but can be resolved by running each appliance at lower levels or buying those that are marketed as “low noise.”
  • Both appliances require continuous maintenance. The filters inside an air purifier can be expensive to replace. The more pollutants it can trap, the more expensive the filter is. Dehumidifiers typically don’t have filters that require to be changed, but you may find yourself having to fix broken parts or to maintain them. For example, the defrosting coils can often stop working if the heating element inside is faulty.
  • Coverage recommendations can be wrong or misleading. I’ll leave this as the final point of discussion below.

The Right Size For the Right Room

There is a lot of confusion about indoor air quality appliances in general and just how large the area that they can cover needs to be. Sadly, there are a lot of misleading recommendations by some manufacturers, as well as poor advice in general.


Air Purifiers

For air purifiers, two things matter. First, how much volume they can cover. This is the square footage of the room times the ceiling height. The second thing that matters is how often they can cycle the air in the room. These two key pieces of information are both necessary to pick the right kind of air purifier.

An air purifier that’s marketed to be able to cover a large volume of space is pointless if the air just sits in the room and is only cycled once per hour. On the other hand, there’s no point in getting an air purifier for a large living room if it’s not strong enough to cycle all the air in it, even if the manual says it can cycle the air every 10 minutes. Sure, it may be able to cycle the air in the room that’s a few feet around it, but will it be able to reach all the air in the room?

When picking the right air purifier, it’s best to look for the CADR rating. This is an industry standard that matches up the capacity of the air purifier to the overall volume of the room. (You may wish to read this post to help you calculate the right size for your air purifier.)



The caveat to dehumidifiers is something known as the AHAM standard, which is short for Association of Home Appliance Manufacturers. This means that basically any feature that’s advertised has been tested under certain conditions, which are a temperature of 80° F and RH of 60%.

But what exactly does this mean for you?

Let’s take a 30-pint dehumidifier that’s advertised to work in a 2,000 square foot space. Most people would rush to buy this dehumidifier for their basements, but in reality, they may need a dehumidifier with a higher capacity.

What if the basement has 1,600 square feet and is measuring at 92% relative humidity (which isn’t as uncommon as most people think)? It means that the 30-pint dehumidifier has a higher starting point as far as the relative humidity is concerned, so it will have to work hard to even get to 60% relative humidity, let alone to keep it at that level or lower.

It’s always good practice to get a dehumidifier with a slightly higher capacity, especially if the room has a high level of moisture already.