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Air Purifier vs. Dehumidifier: What’s the Difference and When Do You Need Them?

Updated on December 15, 2022
Written by
Danny Ashton
Danny is the founder of HouseFresh and has been writing about air purifiers and indoor air quality since 2010. He is our lead tester, conducting all the tests we use to evaluate air quality products. That is why you will always see his name attached to our reviews.

In simple terms, an air purifier is a fan with a filter and a dehumidifier is a fan connected to an evaporating device (to extract water).

You will want an air purifier if you have problems with particles in the air like pollen and other very fine particulate matter known as PM2.5. Fine particulates have the potential to cause serious damage to the human respiratory system according to a large number of peer-reviewed studies, and even low levels can cause problems. Through the use of activated carbon filters, air purifiers can also remove odors and chemical VOCs.

In comparison, a dehumidifier has the sole purpose of reducing the humidity in a space. Many people have issues with high humidity in their basement, a prime example of where a dehumidifier can be beneficial, among other areas.  There has been significant research on the benefits of a humidity range of 40-60 percent according to the Washington Post based on academic papers on the subject of keeping the air free of covid particulate matter.

But what’s the difference between an air purifier and a dehumidifier, and which one makes sense for you? 

We’ll explain everything you need to know to make the best choice for your home.

What Is an Air Purifier?

Air purifiers improve indoor air quality by removing harmful particles from the air circulating in your home. They use filters and sanitizing agents to reduce different contaminants, including:

  • Allergens such as pet dander, dust, and pollen
  • Harmful toxins like volatile organic compounds (VOCs)
  • Smoke and odors
  • Microorganisms such as bacteria and viruses
  • Mold spores

Most air purifiers are light, portable, and slim, so they should easily fit in any room where they are needed. They are available across a wide price range, with some costing under $100 and others exceeding $1000. Depending on the air quality issues you’re facing, you can choose just one or a combination of several different air filters to freshen your home.

HEPA Filters

A high-efficiency particulate air (HEPA) filter is a pleated filter consisting of interwoven fine fibers that form a tight mesh. Air can pass through the mesh, but harmful particles are trapped. An industry standard, HEPA filters are capable of trapping 99.9% of airborne particles less than 0.3 microns in size.

The small filter size means that HEPA filters can capture everything from dust to mold and bacteria, which are commonly around 0.2-1 microns wide. A HEPA filter doesn’t remove everything, but some of the air purifiers for medical usage target bacteria and viruses down to 0.01 microns to filter out even smaller contaminants.

Activated Carbon

Activated carbon, or activated charcoal, is common in air and water filters because it helps to trap and remove harmful gases, odors, smoke, chemicals, and VOCs. Unlike HEPA filters, which generally last 6-12 months, many activated carbon filters will last for more than three years.

The carbon used in these filters is conditioned to give it a large surface area, and this allows it to adsorb more molecules. Unlike absorption, adsorption is the process by which molecules cling to the outside of a surface rather than getting sucked inwards. By maximizing the surface area, there are more places for harmful toxins to stick, and this means that the filters will continue working for as long as possible.

With an activated carbon filter, you can remove odors from everyday household sources like musty carpets, pets, burnt food, or tobacco smoke. These are also ideal if you’re concerned about off-gassing and dangerous chemicals from furniture, mattresses, carpets, or household cleaners.

Although they work well at removing odors and chemicals, carbon filters do not remove many airborne particles, so it’s usually best to use them alongside a HEPA filter.


We don’t recommend UV technology as the science just isn’t supportive of their benefit, with many studies showing that they had little to no effect on how clean the air was – see this comparative study from 2006.

UV-C is used for hospitals as a way to disinfect, but the air would have to be in front of the lamp for a much longer time than is available with a fan pushing it.

There are also many more filter technologies available, such as photocatalytic oxidation, plasma, ozone, and ionization. Ozone really works but can also be incredibly dangerous to human life and so should only ever be used when no one is home. You generally would want to avoid any portable units that generate ozone, which is why we don’t recommend these units.

What Is a Dehumidifier?

A dehumidifier processes air like an air purifier, but rather than filtering out contaminants it removes moisture in order to control humidity. Excess moisture can be irritating and potentially dangerous for several reasons.

Moisture in the air and on surfaces provides a perfect environment for several unwanted guests: bacteria, viruses, dust mites, and fungi spores all thrive when the humidity rises above 60%. This means that dehumidifiers are especially useful for individuals with certain allergies and respiratory illnesses like COPD and asthma.

When moisture is left unchecked for too long, it can allow mold to develop and cause extreme respiratory problems. It will also potentially warp or rot any wooden structures and cause damage to the foundation. A dehumidifier for basement use is common to protect concrete and masonry and prevent mold and mildew from spreading.

And it’s not just the microscopic nuisances you need to worry about. Moisture attracts all types of pests, including cockroaches, earwigs, ants, termites, and more. These pests not only present numerous additional health risks, but they can also cause damage to the home as they set up their nests.

Dehumidifying your basement and crawlspace will take away those ideal nesting conditions, and at the same time, it will prevent rising dampness from ruining your subfloor.

Types of Dehumidifiers

Dehumidifiers vary in size depending on the amount of dehumidifying power you need. Portable roller dehumidifiers can cycle 30-70 pints of moisture every 24 hours, but there are also small dehumidifiers that can be used for convenience in small to mid-sized rooms. You’ll need to measure your space and assess the dampness level to choose the appropriate size.

The two main types of dehumidifiers available to buy use refrigerant or desiccant to lower humidity.

Refrigerant dehumidifiers operate like an A/C evaporator coil to remove moisture: warm, humid air moves through the unit, passing over cool coils that collect condensation and feed it into a tank. Although they work similar to A/C machines, these dehumidifiers don’t lower the temperature inside the house.

Desiccant dehumidifiers use a wheel containing a moisture-absorbing material like silica gel that slowly rotates to dehumidify incoming air. Although it absorbs moisture, an internal heater continuously dries the material, so you don’t have to worry about changing it out. These units are generally quieter than refrigerant models, but they don’t have the same drying power. 

When to Use an Air Purifier

If you want to inhale fresh, clean air, an air purifier is the best way to remove any particles – either visible or invisible. Consider an air purifier for the following situations:

Air purifiers can also help with musty odors and mold but look for high score cadr air purifiers. However, if you have those issues, you’ll need to investigate your moisture issues and likely deploy a dehumidifier first to get to the root of the problem before cleaning the air.

Keep in mind that air purifiers only filter the air and not any contaminants that have settled on surfaces, carpets, or furniture. They won’t replace the need to vacuum and dust, but they may make it a less frequent chore.

You may prefer to pay attention to your habits around the house to decrease the need for an air purifier. By washing your pets, not smoking inside, and using green cleaning products, you can remove many irritants that can impact your health.

When to Use a Dehumidifier

A dehumidifier is an essential tool when you notice various signs of dampness, like heavy air, musty aromas, or condensation on the windows. It’s easy for basements and areas with poor ventilation to become too humid, requiring a dehumidifier.

If you don’t manage humidity, you could face foundation damage, mold growth, pest infestations, and respiratory problems.

Individuals with allergies will be subject to more irritants in humid conditions. Meanwhile, those with asthma need an environment that’s not too dry or too wet in order to avoid an asthma attack. Dehumidifiers with automatic on/off functions are best for keeping the room at the optimal humidity level.

About the author

Danny Ashton

Danny is the founder of HouseFresh and has been writing about air purifiers and indoor air quality since 2010. He is our lead tester, conducting all the tests we use to evaluate air quality products. That is why you will always see his name attached to our reviews.