How to Choose an Air Purifier

Article By:
Max Mutter and Steven Tata

Last Updated:

As we humans become more and more aware of the health hazards that surround us everyday people are looking for ways to mitigate those hazards. Enter the air purifier. These devices offer a simple way to remove particulates, and even some gaseous molecules, from the air in your home. However, choosing the right one, and deciding if one will even benefit you, can be a bit daunting. In this article we outline who will and will not likely benefit from an air purifier and provide a step by step guide for choosing the right model. We also include some more detailed background information, in case you want to dive into the specifics.

A note about ionizing air purifiers
There are a number of models on the market that use ionizers to clean the air. Ionizers essentially emit charged particles that stick to the other particles you'd like to remove from the air, making them easier to catch in a filter. Some of these machines have been found to emit ozone, which can be a very strong lung irritant. Many manufacturers today are advertising ozone free ionizers, but at this point we would tend to err on the side of caution and go with a non-ionizing model instead. A few of the models we tested include optional ionizers. However, we didn't find that the ionizers increased their performance significantly, so we kept all of the ionizers turned off for our final rounds of testing.

Who Can Air Purifiers Help?

Unfortunately there are no definitive scientific studies saying that the portable style air purifiers we tested improve your health. However, they are proven to reduce air particulate concentration, which can often improve day-to-day quality of life for certain subsets of the population.

Airborne Allergen Sufferers

If you're allergic to something airborne, pollen and dust being the most common perpetrators, an air purifier can remove large portions of those particulates from the air. Here again, studies on whether a purifier can actually decrease allergy symptoms are not definitive, but you don't have to look far to find an allergy sufferer who swears by their trusty purifier. We also have a few pollen sufferers in the office that reported better sleep when they took one of our purifiers home. Just remember, allergens can also settle into your carpet, so a good vacuuming is always helpful as well.

Purifiers can help with airborne pet dander and allergens  but you'll also need a thorough vacuuming to get the stuff that has already settled into the carpet.
Purifiers can help with airborne pet dander and allergens, but you'll also need a thorough vacuuming to get the stuff that has already settled into the carpet.

Those with Respiratory Afflictions

The symptoms of most respiratory ailments, like asthma and COPD, can be aggravated by particulates in the air. A good air purifier can reduce airborne particulates in your home and possibility mitigate some of your symptoms. If you're not sure whether air quality is exacerbating your respiratory symptoms, you can track it here.

Who Air Purifiers Likely Won't Help

While purifiers are great at filtering particles out of the air, there are certain things they just can't do, or do poorly.

Those Looking to Control Odors

Odors are generally caused by molecules, which are far too small to be caught by a filter. Many purifiers, including most of the models we tested, have activated carbon filters (in addition to a standard air filter) to get around this problem. Activated carbon creates a chemical attraction to certain airborne molecules and acts like a sponge. However, in our testing none of the activated carbon filters were effective at reducing odors. Though many purifiers brought the airborne particulate counts close to zero, the room still always smelled like smoke. Opening a window was much more effective at getting rid of the odor.

Those Concerned About VOCs

If you're most concerned about volatile organic compounds (VOCs) or other gaseous pollutants most air purifiers will make only a small difference at best. Here again it is an activated carbon filter that would remove such compounds, but one filter won't be able to catch every type of gaseous pollutant. Even the Environmental Protection Agency states that, "…gas-phase filters may remove a portion of the gaseous pollutants and some of the related hazards, at least on a temporary basis. However, none are expected to remove all of the gaseous pollutants present in the air of a typical home." There is some circumstantial evidence that very large carbon filter can be fairly effective, but when it comes to VOCs and gaseous pollutants it is much better to try and remove or mitigate their source than rely on an air purifier.

Those Worried About Germs

Some purifiers use a UV light to kill germs and pathogens in the air. While UV treatments have been proven to be effective in decontaminating water, there is no evidence that using the same technology in an air purifier can improve your health. If it provides you with peace of mind then by all means shine that UV light away, just don't expect it to be a miracle worker.

Choosing the Right Air Purifier

If you've made it through the the first part of this article thinking that an air purifier might be useful for you the following step-by-step guide will help you choose the perfect model.

Step 1: Do You Need True HEPA?

There is a somewhat convoluted and confusing rating system for air purifier filters (more on that below, if you're interested) but the bottom line is this: True HEPA filters can filter almost all airborne particulates while other more inexpensive filters (often called HEPA Type, or sometimes just HEPA) aren't quite as efficient. If you're concerned about things like smoke or some pet allergens that can produce small, hard to filter particulates, you'll want to spend extra on a device that can use True HEPA filters. Pollen consists of substantially larger particles, so if pollen is your main concern you can get likely away with a cheaper HEPA type filter.

The increased performance of True HEPA filters can make a difference with small particulates like smoke.
The increased performance of True HEPA filters can make a difference with small particulates like smoke.

Step 2: Consider Room Size

You'll want to make sure that you get a purifier large enough to effectively clean the air in whatever room you'll be using it in. Air purifier capacity is rated by clean air delivery rate (CADR). You can read more about CADR below, but the general rule of thumb is that you want a CADR that is at least ⅔ of your room's size in square feet. So if you have a 300 square foot room you'll want a CADR of at least 200. This rule assumes standard 8 foot ceilings, so if you have especially high ceilings you may want a higher CADR.

Step 3: Consider Operating Costs

Filters and electricity aren't free, so there is going to be an ongoing operating cost associated with your purifier. You can use our estimated operating cost figures to make sure you find a model that will fit your budget.

The Blueair Pure 211 has the biggest CADR of any of the models we tested  but also has the highest operating cost.
The Blueair Pure 211 has the biggest CADR of any of the models we tested, but also has the highest operating cost.

Step 4: Consider Noise

You'll likely be spending a lot of time next to your purifier while it is running, so you'll want to make sure the noise it makes isn't going to annoy you. None of the models we tested were too loud, nothing that a few clicks up on the TV volume can't drown out, but some were much more noticeable than others. You can use our noise ratings as a guide.

Background Information and Terminology

Here we will dive into the details of some purifier related terminology, in case you want to know what's behind all those numbers and ratings.

True HEPA vs. HEPA Type

First thing is first, HEPA refers to a genre of filter and stands for High-Efficiency Particulate Air (filter). Most air purifiers (or, more accurately, the filters they use) will be rated either as True HEPA or HEPA Type. In the US True HEPA filters are certified to trap 99.97% of particles that are 0.3 microns. 0.3 micron particles are the hardest to filter, so essentially this rating means a filter can remove essentially all particulates from the air.

If a filter is not True HEPA it is often advertised as HEPA Type, or simply advertised with somewhat ambiguous claims such as "removes 99% of airborne particles." These filters likely don't filter efficiently in that difficult 0.3 micron range. Things in that range can include some pet allergens (often it's not the hair but other particles that cause allergic reactions), some larger smoke particles, and some bacteria and fungi. One notable allergen that is well outside that range is pollen, which tends to be between 10 and 100 microns in size. So while these filters won't help for many potentially lung irritating particles, they are likely to help those with pollen allergies.

The smaller the purifier  the closer it will likely be to you. This makes noise even more of an issue.
The smaller the purifier, the closer it will likely be to you. This makes noise even more of an issue.


CADR, or Clean Air Delivery Rate, is a specification that is meant to measure the amount of clean air an air purifier can pump out and is based on independent testing conducted by the Association of Home Appliance Manufacturers (AHAM). The test essentially involves running the purifier inside a room with a volume of 1008 cubic feet for 20 minutes, and comparing contaminant concentration before and after. Three scores are awarded after this test, one for tobacco smoke, dust, and pollen. However, most models score the same or very similarly in all aspects, so the CADR is often reported as a single number.

CADR numbers essentially correlate to the amount of clean air a purifier can pump out each minute. So a purifier with a CADR of 300 is able to produce 300 cubic feet of clean air every minute (more precisely, it achieved airborne particulate concentrations within that 1008 cubic foot room equivalent to adding 300 cubic feet of clean air every minute).

Generally it is recommended that you use a purifier that has a CADR that is at least ⅔ the square footage of the room you would like to use it in. So if you have a 300 square foot room you'll want a CADR of at least 200. Obviously there are a number of confounding factors like how much new air is flowing into your room, significant sources of contaminants, or very high ceilings that would necessitate getting a purifier with a larger capacity, but the ⅔ rule is a good place to start when considering what CADR you need.

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