7 Important Things to Know When Purchasing An Air Purifier

Air purifiers seem to have become all the rage in recent years, and for good reason. With wildfires ravaging many parts of the world, air pollution being the leading environmental cause of death worldwide,1 and indoor air pollutants having been observed to be 2 to 5 times higher than outdoor concentrations,2 it’s not surprising to see people purchasing air purifiers left and right. According to the EPA, we spend 90% of our lives indoors, so it sounds like a smart purchase.

However, it’s important to know the fundamental facts when it comes to air purifiers, because not all air purifiers are created equal.

They seem like such nifty devices with a great promise: to achieve excellent indoor air quality by simply plugging it in, turning it on, and forgetting about it. But, are they too good to be true? How do you pick a good one? Here are 7 very important things to know about air purifiers when using one or purchasing a new one.

1. You can try your best to follow the instructions of the air purifier, but what it can achieve in your home won’t match up to the efficacy it demonstrated in a controlled, laboratory setting.

Simply put, your home isn’t going to perfectly replicate the laboratory in which the air purifiers were tested. There will be size differences in the rooms, airflow differences, and different indoor air pollutants.

A huge tip to help maximize the air purifier’s efficacy is to follow all the instructions as closely as you can, especially when it comes to its placement in the room. This will depend on the type of air purifier it is (tabletop, wall-mounted, floor/tower). Some tips include things like not putting it in the corner of the room, keeping it a certain distance from all walls and the floor, putting it near places with good airflow, and not using it in places with too much humidity.

The best thing you can do is to peruse the manuals that come with the device very carefully and try to determine the places in your home that you can use it.

2. There are 2 standards to look out for in your typical indoor air purifiers: MERV and CADR. They both represent particle removal efficacy. No gas removal efficacy standard has been established.

Air purifiers work by using fans to move air through a series of filters to capture airborne particles. They can be things like particulate matter, some chemical molecules, allergens like dust, pollen, mold, and bacteria. The better the filters are at capturing these particles of various sizes, the more effective the air purifier is. The EPA doesn’t recommend any manufacturer or brand of air purifier, but they do have general guidelines on their site for things to look out for.

Minimum Efficiency Reporting Values (MERV) represent a filter’s ability to capture particles that are between 0.3 um and 10 um.3 The higher the MERV value is, the more effective it is at removing particles of that size range from the air. MERV was established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).4

HEPA filters have been shown to be able to effectively remove particles that are 0.3 micrometers (um) in diameter, which have been established to be the most penetrating particle size (MPPS). They can definitely remove larger particles if they are airborne, and smaller particles that are airborne as well, and the 0.3 um measurement is the standard used simply because it’s the most penetrant.5 The best HEPA filters are known to be MERV 17, and are often found in hospitals and nursing homes. HEPA filters found in indoor air purifiers are anywhere between MERV 11-16.

The Clean Air Delivery Rate (CADR) is a quantification that represents how much smoke, pollen, and dust particles in the air a particular air purifier can remove when run at a certain speed. It was established by Association of Home Appliance Manufacturers, and is recognized by the Environmental Protection Agency (EPA) and Federal Trade Commission (FTC). Portable air purifiers with a HEPA filter achieve a high CADR rating. 450 is the highest a CADR rating can be.

There is no rating scale for gas removal, though,6 and so far, nothing has been established for gaseous pollutants, radon, and other related molecules. An activated charcoal component may be effective at removing some gaseous pollutants, although the research isn’t as established as with particulate removal.7

The main points:

  • Consumers can compare the MERV and CADR scores across devices to see what suits their space and needs.7
  • The device you select should have a substantial activated charcoal component, which can help remove unwanted gases from the air, in addition to having a HEPA filter that removes the particles from the air.6
  • The EPA doesn’t recommend any particular brand, model, or manufacturer of air purifier or air cleaning device.8

3. A lot of allergens aren’t airborne and won’t be captured.

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Even the best air purifiers aren’t going to take in all of the allergens that are sitting on your countertops and upholstery. They aren’t airborne, and they won’t be handled by air purifiers. It’s important to regularly clean high-traffic upholstery and surfaces in your home so that they don’t accumulate allergens that may affect you.

This will depend on what you’re allergic to. Your allergist should be able to provide you with more informed directions on how to avoid severe symptoms and may have recommendations for you regarding purchases to make, such as bedding and furniture covers.

If you want a reliable air purifier that really cleans the air as best as it can, without running on “high” and making a lot of background noise, go for a larger size than what’s recommended for your room’s size. That way, you’ll be able to run it on a quieter setting, and still be confident that it’s properly processing the air in your room.

5. Avoid ones that generate negative ions/ozone!

Certain air purifiers have a selling point that says they can generate ions that can influence the amount of air pollution in a room. They do this by using electricity to generate negatively or positively charged ions, which stick to the particles in the air. This leads to some of the particles being displaced from their airborne state and ending up on the floor or surfaces, which prevents them from being inhaled. However, abrasion can lead these molecules to end up in the air, and only very small molecules have been shown to be affected by this technology.9

Ozone: “Good up high, bad nearby.”

In addition, ozone is generated as a byproduct in this process, and the levels of ozone that end up in the air can be much higher than recommended.10 Some air purifiers actually advertise ozone production as a way to help with odor control. Be warned, though: the levels of ozone required to clean the air in any of these cases is much higher than what has been established as healthy for humans, so it’s best to not rely on ozone for any sort of air purification.

Don’t be fooled by advertising stating things like “air cleaning”, “energized oxygen”, and “pure air”. Ozone is not a good gas to have around, and it’s totally different from oxygen, chemically and toxicologically.11 As the EPA says, ozone is “good up high, bad nearby”.12

6. Change the filters often.

This might sound obvious, but it’s pretty common for people to not change their air purifier’s filters as often as they should. Filters should be changed at least as often as the directions on your particular machine state, and it’s usually every 3-6 months or so. Definitely purchase backup filters on a regular basis once you find an air purifier that addresses the concerns (allergy symptoms, smells, smoke) that you are satisfied with. 

7. Other environmental controls are effective too: kitchen exhaust fans, bathroom fans, windows, and regularly cleaning surfaces.

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You are responsible for the air quality in your home. It’s in your control, and an air purifier isn’t the only or the best way to maintain clean indoor air.

You can check the air quality outside by using a variety of online tools (airnow.gov is a good one) and if it’s acceptable, definitely keep windows open and allow regular airflow. You can use kitchen exhaust fans and bathrooms exhaust fans as well to remove odors and air from spaces in your home.

This is especially important in the winters when we have the windows closed more often. Indoor air pollution can get bad pretty quickly through the combined use of fireplaces, candles, cooktops and grills, cleaning supplies, and carbon dioxide.


There are a lot of reasons why one would consider purchasing an air purifier. It can be to alleviate allergy symptoms, to eliminate odors from something indoors or outdoors, or to just have something that’s helping give you peace of mind for general indoor air pollution. Whatever the reason may be, it’s very important to consider indoor air quality in your everyday life.

Have you purchased an air purifier recently, or are you thinking of getting on sometime soon? It’s important to keep these tips in mind as you make your purchase. I hope this list helps you find one that suits you needs well!

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