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 their pros and cons, including Clean Air Delivery Rate (CADR), room-size ratings, air changes per hour (ACH), HEPA, “True HEPA,” “HEPA-type,” “HEPA-like,” “HEPA-style,” “99% HEPA,” H13/H14 HEPA, “HEPAsilent,” and HyperHEPA.
What is Clean Air Delivery Rate (CADR)?
Clean Air Delivery Rate (CADR) was developed by the Association of Home Appliance Manufacturers (AHAM) to help consumers compare how quickly portable air purifiers reduce airborne particles. AHAM represents appliance manufacturers, and participation in its verification program is voluntary. CADR applies to stand-alone room air purifiers, not whole-house filtration systems.
CADR is expressed in cubic feet per minute (cfm). It describes how much equivalent clean air a purifier delivers, based on the rate at which particles disappear from a test chamber after accounting for their natural decline. In AHAM’s 1,008-cubic-foot chamber, the purifier receives separate ratings for tobacco smoke, dust, and pollen. Smoke and dust tests last 20 minutes; the pollen test lasts 10. A higher CADR means faster removal of the tested airborne particles under those conditions (1).
The CADR rating system has many weaknesses that dramatically limit its usefulness, including:
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It does not show long-term performance. A test lasting 10 to 20 minutes cannot show how a purifier performs after weeks or months of real-world use. Air purifier performance can degrade over time depending on environmental factors and a variety of indoor air pollutants that laboratory testing can’t capture (2).
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It does not give a separate rating for ultrafine particles. Tobacco smoke represents the smallest particles in the standard CADR tests, but its test range begins at about 0.1 microns. CADR does not report performance at each size below that point. Ultrafine particles can make up much of the particle count in ambient air, so consumers concerned about them should look for particle-size-specific test results.
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It does not measure removal of gases, chemicals, or odors. The familiar smoke, dust, and pollen CADRs measure particles, not volatile organic compounds (VOCs) or odors. AHAM has published a separate standard for chemical reduction, but a particle CADR does not convey those results.
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It does not show where particles go. CADR measures a reduction in airborne particles. Some ion-generating devices charge particles so they collect on walls or furnishings rather than in the purifier. Deposited particles can later be stirred back into the air. The EPA also notes that charging particles may affect how they deposit in the respiratory tract.
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The CADR number does not measure ozone emissions. Avoid air cleaners that intentionally generate ozone in occupied spaces. Ozone can irritate the lungs, and some electronic or ionizing cleaners may emit it as a byproduct.
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It may not reflect the speed used every day. A published CADR is typically measured at the highest setting, while many people use a quieter speed. The headline number does not show how quickly the purifier removes airborne particles at low or medium settings. Particle-removal rates and noise levels measured at each fan speed give a clearer picture of its performance in daily use.
These limitations make CADR an unreliable measure of an air purifier’s overall performance. For this reason, IQAir does not consider CADR a valid standalone method for evaluating air purifiers and does not participate in AHAM’s rating program.
Room size ratings
Many air purifiers are advertised as suitable for a specific room size. These ratings are usually calculated directly from CADR. Under AHAM's guidance, multiplying the smoke CADR by about 1.55 gives the recommended maximum room area, assuming an 8-foot ceiling. In theory, a unit with a CADR of 100 would be suitable for a room of about 155 square feet. At that room size, AHAM’s calculation assumes roughly 4.8 equivalent clean-air changes per hour (3).
Because room-size ratings are derived from CADR, they inherit all of its limitations. They reflect a new unit running at its highest speed for a short test, so they say nothing about how well the unit will serve that room after months of use, at a quieter fan setting, or against ultrafine particles and gases. Rooms with higher ceilings, open floor plans, or heavy pollution sources also need more cleaning capacity than the rating suggests.
When sizing an air purifier, it is more useful to consider effective air changes per hour (ACH), or how many room volumes’ worth of clean air the unit delivers each hour, at the fan speed you will actually use, alongside verified filtration results for the particle sizes of concern.
What is High Efficiency Particulate Air (HEPA)?
The acronym “HEPA” stands for High Efficiency Particulate Air, a type of air filter originally designed in the 1940s to protect workers developing the atomic bomb. The filter was designed to control tiny particles contaminated with radioactive material. HEPA filters work in mechanical air purifiers and are often 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 0.3 microns in diameter to qualify as HEPA. This is a particularly difficult particle size to capture; HEPA filters also capture particles smaller than 0.3 microns.
Therefore, “HEPA” refers to both a type of filter technology and an efficiency standard. Due to its high efficiency, reliability, and proven track record, HEPA technology has become an industry standard for particulate filtration in critical environments, such as laboratories and hospital operating rooms.
Recognizing the great marketing potential of the term “HEPA,” many manufacturers use it to project a high-performance image onto their room air purifiers. The problem is that a filter’s HEPA rating does not necessarily tell consumers how the finished purifier performs. Air can leak around a poorly fitted filter, and damage during manufacturing or use can also affect performance.
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,” H13/H14 HEPA, and “HEPASilent” are some of the terms consumers are faced with deciphering.
“True HEPA” is a marketing term designed to assure customers that a filter meets the HEPA standard, but the words themselves are not a certification. “HEPA-type,” “HEPA-like,” and “HEPA-style” are weak claims because they identify no tested HEPA grade. A “99% HEPA” claim falls short of the U.S. HEPA benchmark of 99.97% at 0.3 microns if measured under the same conditions. H13 and H14, on the other hand, are genuine HEPA filter classes under a different standard, with H14 the stricter grade. HEPASilent is a branded filtration technology that has demonstrated HEPA-level filter efficiency in independent testing. Whatever the label, a filter result alone does not verify the performance of the complete air purifier (4).
Some so-called HEPA filters are made of ordinary synthetic fibers, which should not be assumed to perform like tested HEPA media. Other air cleaners use electrostatic particle charging or ionization. Ionizers should be avoided because they can deposit charged particles on room surfaces, and some produce ozone. Particle-collecting plates can also become loaded and lose efficiency if they are not cleaned. Charged filter media can lose efficiency over time, too: in one study of ventilation filters, efficiency fell by nearly 50% after just 11 weeks of use.
Is “True HEPA” truly the gold standard?
Filters that achieve the HEPA standard remove at least 99.97% of particles 0.3 microns in diameter. This is a particularly difficult particle size to capture, not the smallest size a HEPA filter can remove. Airborne particles are categorized into several sizes, including coarse, fine, and ultrafine. The smallest particles ultrafines can make up around 90% of airborne particles by number in some settings and are of particular health concern.
Ultrafine particles are smaller than 0.1 microns and include particles as small as 0.003 microns. Once inhaled, they can reach deep into the lungs. A small fraction can pass into the bloodstream and travel to other organs, including the brain (5).
The U.S. HEPA benchmark specifies filter efficiency at 0.3 microns, while H13/H14 filters are tested at their most penetrating particle size. Neither result alone establishes the complete purifier’s efficiency.
What is HyperHEPA filtration technology?
HEPA is an established standard for high-efficiency particle filtration. IQAir’s patented HyperHEPA filtration technology takes it a step further by filtering ultrafine particles down to 0.003 microns, 100 times smaller than the 0.3-micron particle size used for the conventional HEPA benchmark.
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 make a meaningful difference to the air you breathe. To make an informed choice, look beyond marketing jargon and headline ratings. Consider which pollutants you need to remove, whether performance has been verified for the complete purifier, and how well it works at a fan speed you will actually use.
Frequently Asked Questions (FAQs)
Is a higher CADR always better?
A higher CADR means an air purifier removed the tested particles faster under test conditions, usually at its highest fan speed. It does not show how the purifier performs after months of use, at a quieter speed, or against gases and odors. CADR should not be the only basis for choosing a purifier.
How can I tell if an air purifier's performance claims are trustworthy?
Look for independent testing of the fully assembled air purifier, not just its filter, with efficiency data for particles below 0.1 microns. Check for proven long-term performance, a substantial activated carbon filter for gases and odors, and no ionizers or ozone generation.
How is HyperHEPA different from HEPA?
HEPA filters are rated against a 0.3-micron benchmark, although they also capture smaller particles. IQAir’s HyperHEPA filtration has been independently tested to capture at least 99.5% of particles down to 0.003 microns. IQAir also measures performance in the assembled air purifier, giving consumers information beyond just the filter rating.
Does “True HEPA” mean the entire air purifier removes 99.97% of particles?
No. "True HEPA" refers to a claimed filter efficiency of at least 99.97% at 0.3 microns. It does not verify the performance of the assembled air purifier. Terms such as "HEPA-type" and "HEPA-like" do not show that a filter meets the HEPA standard at all.
