What’s CADR and What’s the Difference With Airflow?

When buying an air purifiers, the terms ‘airflow’ and CADR are often used interchangeably to describe an air purifier’s performance. But what’s the difference between CADR (clean air delivery rate) and airflow? Are they the same thing? Or which one – CADR vs. airflow – should be used when buying an air purifier?

Are CADR and Airflow the Same Thing – Short Answer

In short, CADR and airflow are not the same thing. They are slightly different measurements. That means CADR values from one air purifier should not be compared with airflow values from another air purifier. CADR is typically lower than airflow. We’ll get into that later.

However, if a company claiming that their air purifier has the same CADR and airflow values, then it’s likely this company isn’t providing the full picture.

Read More: How we test out air purifiers at Smart Air

What’s the Difference Between CADR and Airflow – Long Answer

The real answer gets into some nerdy (but actually profound) details about how CADR and airflow are measured.

Here’s what you need to do for a CADR test:

(For total nerds, the government guidelines describe the full methods [in Chinese])

Steps to Test an Air Purifier’s CADR

Step 1: Pollute a sealed room to crazy high pollution levels (normally by lighting cigarettes).

Step 2: Run your purifier.

Step 3: Take PM2.5 concentration readings every 2 minutes for 20 minutes.

Step 4: Use these numbers to work out the rate of purification of the room (the CADR).

The hard part about doing this test is that you need a lot of complex equipment, a large testing room, the time and patience to do the test, and some data analysis skills.

Testing Air Purifier Airflow

To measure airflow, the only thing you need is a wind speed measure (fancy name “anemometer”):

Steps to Test Air Purifier Airflow

Step 1: Place the anemometer against the filter and look at the number.

Step 2: Multiply this speed by the area of your filter.

That’s it! So much easier.

This method works all right, but it has a problem. Since this method only measures wind speed, it only tells us how much air is coming out.

What Airflow Tests Don’t Tell Us

  1. How clean is that air coming out?
  2. Is any of that air actually coming in from a leak or the middle of the air vortex and then being pushed back out?
  3. How efficiently is the machine mixing that air in the room?
  4. How much of the air that comes out of the purifier gets sucked back into the machine quickly, rather than being pushed farther out into the room?

Airflow tests assume perfect values for all of these variables. For example, it assumes that all the air coming out is 100% clean. Because all the assumptions are rosy, airflow values tend to be much more impressive than CADR.

Read More: Can you convert airflow to CADR?

Bottom Line: Airflow vs. CADR

Airflow is less rigorous than CADR and will almost always be much higher than CADR. Do not directly compare the two numbers.

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Comparing Air Purifiers Before Making a Purchase

How to choose: When comparing purifiers, look for CADR over airflow (and pay attention to whether the company is reporting one or the other). CADR tests are often done by third-party testing companies, so may be more reputable. Whereas airflow is typically measured by the purifier manufacturer.

Learn more: The Four Steps to Choosing the Best Air Purifier »


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