June 25, 2021
If you've been shopping for air cleaners, you've probably run across the acronym "CADR" a whole lot. More than likely, none of the listings you've read have anything explaining what CADR actually means. So we're here to help.
CADR stands for Clean Air Delivery Rate, which was created by the Association of Home Appliances Manufacturers (AHAM) to standardize air purifier performance through testing. See, before CADR existed air purifiers simply listed their maximum air flow. Maximum air flow is a great thing to know, but filters aren't 100% effective. CADR measures exactly how much smoke, pollen, or dust is being cleaned by an air purifier in a controlled environment. It turns out that CADR for smoke (the finest particles) tends to be around 2/3rds of the maximum air flow. But why?
Well, air flow isn't the whole story. The HEPA filter and fan have to work together, and filters are designed to work at a certain air flow. Different devices take in air in different ways, which can affect performance.
To calculate CADR, an air cleaner is placed in a room measuring 1,008 cubic feet. The device is then run for 25 minutes, after which the levels of the three contaminants (smoke, pollen, and dust) are measured against the pre-test levels. In this way, an objective measure of how well the air cleaner removes the different particle sizes can be calculated.
Complicating things further are the different units of measure used for air flow and CADR. In the United States, cubic feet per minute (CFM) is the standard unit of measure, whereas meters cubed per hour (m³/h) is common elsewhere in the world. Beware the many manufacturers that do NOT include their unit of measure when listing their CADR! 1 CFM is equal to 1.7 m³/h. If an air purifier seller isn't listing the unit of measure, it is safe to assume that they are using m³/h instead of CFM, or maybe even something worse!
One thing that CADR doesn't tell you anything about are gases and volatile organic compounds (VOCs), nor does it discern between units that use other methods of air purification (like UVC light). If gases or VOCs are a potential concern in your home or office, make sure that you are looking at purifiers that include an activated carbon filter alongside the HEPA filtration.
Not all HEPA filters are created equally either. There are multiple levels of HEPA efficiency, and using a lower efficiency filter can actually RAISE the CADR score of the device! It is easier to move air through lower quality HEPA filters which allows them to create a higher air flow and pass the test more easily. High quality, hospital grade HEPA filters are those which are H13 and higher. An H13 air purifier that also possesses a high CADR indicates a powerful fan that is capable of pulling a large volume of air through the very dense filter.
Bottom line: CADR isn't everything, but it does give you a good idea of how much air a machine is capable of cleaning--to a reasonable degree--within a certain amount of time. Other features, such as a UVC light, activated carbon filtration, air quality indicators, and more may be even more important to you and your family.