Why Can’t CADR Values over 800m3/hr or 450cfm Be Measured Reliably?

The CADR test is an industry standard number to compare the performance of air purifiers. There are two common standards for measuring CADR, they are the AHAM AC-1 standard in the US, or the GB 18801-2015 standard in China.
Both these standards test air purifiers in an empty room of average size. That’s 30m3 for GB 18801 and 1008ft3 or 28.3m3 for the AHAM standard.

When purifiers that are designed for much larger spaces are tested in this standard room size, they clean the entire air in the room extremely quickly, often in fewer than 5 minutes. With air being cleaned so quickly, there is no way to use the standard CADR formula to calculate a CADR value for the purifier. As such, CADR values are limited by the standard size of the testing room, and the formula and method in which CADR is calculated.

For the China GB 18801-2015, the maximum CADR value that can be tested is 800m3/hr;

For the AHAM AC-1, the maximum CADR value that can be tested is 400cfm (680m3/hr) for dust, and 450cfm (764m3/hr) for pollen and cigarette smoke.

Here are the specifications from the AHAM AC-1 standard:

AHAM AC-1 maximum CADR theoretical testing values

Air purifiers that have CADR values above these ranges are shown in independent 3rd party test reports as >800 or >450. For example:

Test Report showing air purifeir CADR value exceeding maximum theoretical CADR

Couldn’t You Just Test the Purifier in a Bigger Room to Measure a Higher CADR?

This is certainly possible, and may give a perceived ‘higher’ CADR value. However, by doing this, the CADR test no longer meets the testing standard specifications. That means that the CADR value produced from this test can’t be used to compare CADR against other purifiers.

Does that Mean that Companies Marketing Air Purifiers With CADR Values over 800m3/hr or 450cfm are Lying?

If a company modifies the standard testing method to measure higher CADR values, then they could test and publish any CADR value they like. But this would mean that the CADR value they give cannot be used to compare against other purifiers.

For example, when Smart Air tested the Smart Air Blast Air Purifier in our lab, we found a CADR value of 890m3/hr. However, we make clear that this value was tested by Smart Air in house.

Using Real World Tests as a Way to Validate High-CADR purifiers

For cases where purifiers are required for large spaces over 100sqm, we recommend performing real world tests to ensure maximum cleaning efficiency.

For example, Smart Air’s Blast and Blast Mini air purifiers are powerful purifiers designed for large spaces. Smart Air can provide after-sales services including real world testing to make sure you are receiving the best clean air possible with your purchase.

Are There Any Other Measurements I Can Use When Purchasing an Air Purifier?

Other than CADR, an air purifier’s air flow rating and air changes per hour can also be used to estimate a purifier’s effectiveness in your room.

Learn more about air changes per hour and how to calculate it here »

Learn more about the differences between air purifier airflow and CADR here »


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Smart Air is a social enterprise that creates simple, no-nonsense air purifier and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.