What exactly is CADR?

Choosing an air purifier is no easy task. As warnings about the effects of poor indoor air quality flood the public sphere, concerned customers scramble to find the right air purifier for their needs. A rating such as CADR might seem like a good way to compare products, but it can be misleading. 

The abbreviation “CADR” stands for Clean Air Delivery Rate. The rating was developed in the early 1980s by the Association of Home Appliance Manufacturers (AHAM) and has become one of the standard ratings in an unregulated air purification market. It does, however, remain a voluntary program that manufacturers can join for a fee. It applies only to portable room air purifiers, not whole home air cleaning systems. These require a different measuring system such as MERV (Minimum Efficiency Reporting Value) for A/C air filters.

Once manufacturers become part of the program, they certify the room air cleaner. The association says that an independent laboratory verifies the performance of random samples taken from factory, warehouse and dealer showrooms. If the results do not match the claims, the units are not allowed to display the certification sticker.

In order to get a CADR rating, the air purifier is ostensibly tested in a closed-off room of 1008 cubic feet for 20 minutes. The contaminants in the room are measured before, during and after the test.

The CADR seal then provides a suggested room size for the air cleaner (using a specific formula based on the test results) and three different metrics that reveal how well the unit removes smoke particles, pollen and dust from that room in 20 minutes.

These numbers are related to the CFM (cubic feet per minute) capabilities of the unit.

The higher a number, the larger the amount of air that is being filtered in that particle size range. Smoke particles are the smallest and most dangerous, while dust particles are larger and considered less dangerous.

The rating does not measure the particles that are falling out of the air naturally and landing on the room’s surfaces and floor.

How is CADR used to compare products?

The association suggests comparing the numbers on the seal and to first make sure the room size is comparable.

Next, take note of the tobacco smoke, dust and pollen CADR numbers. Higher numbers mean quicker filtration. The air filtering performance is similar if the numbers are similar.

It is pretty much impossible to get high numbers for all three particle ranges because of different airflow requirements.

For example, if an air purifier gets a high rating for smoke particles because it is using a slow fan, then the CADR numbers for dust and pollen are bound to be lower. That’s because pollen and dust are larger particles that will fall down and deposit on the room surfaces before the air purifier can collect them during the 20-minute test.

Conversely, if an air purifier gets high numbers for pollen and dust, it may not be as efficient to remove smoke particles.

By the numbers

            Smoke                        Pollen                         Dust

Particle sizes               0.09–1.0 microns        5–11 microns              0.5–3 microns

CADR ranges             10-450                         25-450                         10-400

Adversities of the CADR Verification Program

While the CADR ratings may be valuable in some ways to compare units that filter out particles, air purification experts have warned that the system has its limits as well:

• Chemical ignorance: One of the problems of the CADR rating is that is applies only to airborne particles that are being removed. But studies increasingly identify airborne chemicals as the most worrisome with regards to health and well-being. That is why many manufacturers of air purifiers focus more on the removal of volatile organic compounds and gases that requires different filtration media such as activated carbon.
  Even though these units may also employ high-efficiency particulate filters, activated carbon air purifiers often come with the recommendation of using them at a low speed to make sure the chemicals and gases have a chance to chemically attach themselves to the activated carbon. Of course, in order to receive a high CADR rating, the units would have to run at a higher speed and in these cases the ratings become an inadequate way of measuring an air purifier’s overall filtration capabilities.
  
• Danger of the smallest particles: Another concern is that the CADR fails to advise people on an air filter’s ability to remove very small particles. Very small particles are the most common and researchers have identified them as the most dangerous to human health. That’s because they can easily enter the bloodstream through the lungs when they are breathed in.
  Unfortunately, people may choose an air purifier based on a high CADR rating for pollen and dust, but their units are often unable to capture the smallest particles.
  
• The high setting conundrum: During the 20-minute test, air purifiers run at the highest speed, which is not likely to happen in people’s homes or offices. Noise considerations usually mean that users choose a lower speed. In some cases, as in the carbon air purifiers mentioned above, a lower speed comes recommended anyways. Even particle filter makers oppose high speed settings: Manufacturers warn that running a HEPA filter at high speed for prolonged periods of time may damage the filter’s mat of fibres. That means that the CADR rating may not be accurate when an air purifier is actually used, since running an air purifier at a lower speed can also alter the unit’s filtration capabilities.

• Effectiveness over time: The CADR applies only to new filters and does not take into account a unit’s effectiveness over time. A HEPA filter, for example, could actually become more effective over time, while other filters may lose effectiveness.

So, yes or no to the CADR program? There is no easy answer to that question. The CADR certification has become a standard for particle filtration units on the market, but customers looking for the right air purifier need to make sure that the rating addresses all of the airborne contaminants they are concerned about. It may be best to contact the manufacturers and ask your questions.