Three air purifiers positioned in a row.
Three air purifiers positioned in a row.
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Which air filter rating should you trust?

There are several air filter ratings systems. This can make it difficult for consumers to know who or what to trust. Learn about the different ratings systems, terminology, and the pros and cons.

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There are several air filter rating systems. This can make it difficult for consumers to know who or what to trust. Learn about the different rating systems, terminology, and the pros and cons, including Clean Air Delivery Rate (CADR), room-size, HEPA, “True HEPA,” HEPA-type,” “HEPA-like,” “HEPA-style,” “99% HEPA,” “HEPAsilent,” and HyperHEPA.

Clean Air Delivery Rate (CADR)

Clean Air Delivery Rate (CADR) ratings were developed by the Association of Home Appliance Manufacturers (AHAM) in the 1980s as a way for the general public to navigate the claims made by air purifiers. AHAM is an organization representing household appliance companies. 

The CADR rating is meant to be a standard represented by a numerical value that allows consumers to measure the effectiveness of stand-alone air purifiers (CADR ratings are not used for whole-house systems). Theoretically, it is a measurement of particles removed multiplied by the airflow rate (cubic feet per minute or CFM) passing through the device.

There are three CADR ratings given the AHAM seal: dust, pollen, and tobacco smoke. AHAM uses a test space of 1,008 cubic feet in its CADR performance reviews (11′ x 11′ x 8′ room). Dust, pollen, and tobacco smoke pollutants are introduced into the test space, and brand new air purifiers are turned on for twenty minutes (testing for pollen ends after only ten minutes). After running for this short time, the remaining contaminants are tested and converted into the final CADR rating.

The CADR rating system has many weaknesses that dramatically limit its usefulness, including:

  • CADR only tests performance for no more than the first twenty minutes of operation, which provides no basis to evaluate long-term performance. The absurdly short test cannot account for the performance decline of most air purifiers over time. The majority of air purifiers offered by manufacturers belonging to AHAM start losing efficiency after only one hour of usage. In fact, a leading hybrid air purifier lost 50% of its efficiency after only 8 weeks of testing. Learn more about how IQAir tests for long-term efficiency here.
  • CADR does not test performance against ultrafine particles – smaller than 0.1 microns – that make up more than 90% of all particles in the air and pose the most health risk. Many AHAM air purifiers have trouble filtering ultrafine particles effectively. A rating that does not measure the ability of an air purifier to eliminate the most numerous and most dangerous particles cannot be trusted.
  • CADR does not test effectiveness for harmful gases, chemicals, and odors. Most AHAM air purifiers do not effectively reduce gaseous pollutants and odors, if at all. Consumers are left without knowing whether the tested air purifier has any gas-phase filtration that is capable of removing harmful gases, chemicals, or odors such as ozone and VOCs. People who suffer from multiple chemical sensitivity (MCS) should never trust CADR ratings.
  • CADR does not distinguish whether an air purifier eliminates particles or deposits them on room surfaces. This is critical to note because it is precisely how ionizers work. The U.S. Environmental Protection Agency (EPA) warns that ion-generating air purifiers can increase the risk of particles being deposited into your lungs and absorbed into your bloodstream. Ion-generating machines can also produce ozone as a byproduct. The American Lung Association specifically recommends avoiding machines that add ions or ozone to the air. Much of the efficiency of AHAM air cleaners comes from depositing particles on room surfaces. 
  • CADR does not measure ozone filtration or production. There is a category of air cleaners that deliberately produce ozone as the primary cleaning mechanism. Ozone is a primary component of smog and can irritate the lining of the respiratory system, causing coughing, chest tightness and shortness of breath. Long-term exposure can cause or worsen asthma and even lead to premature death. Such a dangerous pollutant must be considered for a valid rating system.

For these reasons, IQAir does not consider CADR to be a valid methodology for evaluating air purifiers and does not participate in the rating program. 

Room size ratings 

Room size ratings are problematic because they are based on CADR ratings. According to AHAM, a CADR rating multiplied by 1.55 will provide the room size limit an air purifier can handle. 

Room size ratings are problematic because they are based on CADR ratings.

This calculation is based on a ceiling height of 8 ft. For example, in theory, a 100 CADR air cleaner will clean a room size of 155 sq ft. Any calculation based on a CADR rating is invalid.

High Efficiency Particulate Air (HEPA)

The acronym “HEPA” stands for High Efficiency Particulate Air, a type of air filter that was originally designed in the 1940s to protect workers developing the atomic bomb. The filter was designed to control tiny particles that had become contaminated by radiation. HEPA filters work in mechanical air purifiers and are made with randomly arranged micro-glass fibers. As defined by the U.S. government, HEPA filters must remove a minimum of 99.97% of particles that are more than 0.3 microns in diameter to qualify as HEPA. Therefore, “HEPA” refers to both a type of filter technology as well as an efficiency standard.  

Due to its high efficiency, reliability and proven track-record, HEPA technology has become the industry standard for particulate filtration in critical environments, such as laboratories and hospital operating rooms. 

Most so-called HEPA filters are never tested! 

However, there are not requirements that household air purifiers are tested to meet HEPA standards. Recognizing the great marketing potential of the term "HEPA," many manufacturers use the term “HEPA” to project a high-performance image onto their room air purifiers. The problem is there is that there are no regulations regarding the use of “HEPA” in testing and labeling products. In other words, no independent body is required to test or verify the HEPA claim. Thus, most so-called “HEPA” filters are never tested!  

To confuse consumers further, there are more and more types of HEPA claims entering the market. “True HEPA,” HEPA-type,” “HEPA-like,” “HEPA-style,” “99% HEPA” and “HEPAsilent” are some of the HEPA claims consumers are faced with deciphering. To summarize, true HEPA refers to HEPA filters that claim to capture 99.97% of particles down to 0.3 microns. “True HEPA” is a marketing term designed to assure customers that their HEPA filters actually stand up to HEPA standards. The use of this term is also not regulated. HEPA filters are somewhat fragile, so there’s no guarantee a filter that passes HEPA standards will perform after manufacturing. 

HEPA-type, HEPA-like, HEPA-style, 99% HEPA and HEPAsilent are all subpar versions of what truly constitutes a HEPA air filter.

HEPA-type, HEPA-like, HEPA-style, 99% HEPA and HEPAsilent are all subpar versions of what truly constitutes a HEPA air filter and may never have been tested. Aside from doing your own testing, there’s no way to know how efficient -- or inefficient -- a filter using one of these terms is. 

Some so-called HEPA filters are made of ordinary synthetic fibers. Synthetic fiber media is a far less dense structure and is much less efficient at trapping particles than media made of fiberglass or specialty synthetic fibers. Other filters trying to be passed off as HEPA use electrostatic particle charging, or ionization. As discussed on page X, technologies using ionization should be avoided because charged particles can pose a health threat. Also, particle-charging causes a trapping plate to quickly become “loaded,” and the air purifier efficiency often decreases by even 50% in just a few months. 

Is “True HEPA” truly the gold standard?

The best-case scenario for filters that actually do achieve the HEPA standard is to filter particles down to 0.3 microns at 99.97% efficiency. Airborne particles are categorized into three sizes: coarse, fine, and ultrafine. The smallest particles -- ultrafine -- are the most abundant (90% of all airborne particles) and the most dangerous. 

Why does the air purifier industry tout 0.3 microns as the best in air purification?

Ultrafine particles range from 0.1 microns all the way down to 0.003 particles -- the tiniest that exist. Ultrafine particles are so small that, once inhaled, move straight through the lung tissue and directly into the bloodstream. These dangerous particles then are carried with the blood to where ever it travels, including all major organs -- even the brain!

HEPA filters, at best, test filter paper at 0.3 microns, but not the air purifier’s total system efficiency. Why does the air purifier industry tout 0.3 microns as the best in air purification? Why do so many manufacturers try to mislead the public into believing their filters can actually achieve a standard that doesn’t even begin to touch the smallest, most abundant, and most dangerous particles -- ultrafines? 

HyperHEPA filtration technology

There is one air purification company that has managed to solve the reliable performance problem. IQAir’s patented HyperHEPA filtration technology is able to filter the dangerous and highly abundant ultrafine particles all the way down to 0.003 microns -- that’s ten times smaller than a virus and 100 times smaller than a HEPA filter in the best scenario. 

IQAir’s HyperHEPA filtration is tested and certified by an independent, third-party laboratory to ensure it is effectively filtering ultrafine particles down to 0.003 microns. 

The takeaway

The right air purifier can change your life for the better. The wrong one can actually harm you. Arm yourself with the knowledge you need to make an informed decision. And remember to look beyond the marketing jargon and flawed test processes. For more information, download the Consumer Buyers’ Guide.

Air Quality Life is brought to you by IQAir, a global air quality information and technology leader since 1963. With actionable insights based on the latest air quality research and information, we seek to advance awareness about the impact of air pollution on health.

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