ACH and CADR Ratings Explained

In this article we’ll answer two questions:

By the end of the article you’ll discover why ACH and CADR Ratings are the two most important specifications to look for in an air purifier.

CADR Rating

What is an CADR Rating?

CADR stands for clean air delivery rate. The CADR shows how quickly the air purifier can clean the air within a particular sized room. For example, an air purifier with a CADR rating of 400 cfm will be clean a 400 square foot room faster than a 300 cfm CADR rated air purifier.

The CADR rating is measured in cubic feet per minute (CFM) or m³/hour. CADR ratings are separated into three categories: smoke, dust and pollen.

Smoke particles are ultra fine particles with size ranging from 0.1 to 0.3 microns.

Dust particles are common particles with size ranging from 0.5 to 3 microns.

Pollen particles are large particles that cause allergies with size ranging from 5 to 11 microns.

AHAM Rating Seal

The AHAM (Association of Home Appliance Manufacturers) tests and rates air purifiers and air cleaners. There are 3 types of airborne contaminants with a CADR rating:

  • Tobacco Smoke (10-450 CADR)
  • Dust (10-400 CADR)
  • Pollen (25-450 CADR)

The CADR rating will always be displayed as a set of 3 numbers 150 / 160 / 165

For example: The Germ Guardian AC4100 is designed for small rooms and apartments. It has a CADR rating of 50 | 56 | 76.

The AHAM seal is important when you are buying an air purifier. Manufacturers can make claims about the maximum room size but without the certification, there is no guarantee that what they list is true. Its worth it to consider this to find out whether the air purifier is a good deal or not.

Ideally its best to choose the product with the AHAM seal over ones that don’t

*A quick tip – the maximum room size number is roughly 1.5x the CADR rating for smoke. For example a 150 / 160 / 165, where 150 represents tobacco smoke, 150 * 1.5 = 225 square feet

The next most important specification for an air purifier is the ACH rating.

What is ACH Rating?

The ACH rating inidicates how air changes per hour an air purifier can exchange air within a room. More fresh air exchange equals better indoor air quality.

For example, an ACH rating of 4x means that the full air volume is exchanged four times every hour.

When you’re comparing devices the ACH rating will give you a clear indication of which device is better. The bigger the number the more fresh air you’ll clear per hour.

A 2x rating is worse than a 3x rating, while a 5x rating is better than a 4x rating.

ACH Rating

The ACH combined with the CADR rating will be able to tell us how powerful the air purifier is. Lets look at an example below:

You own the Winix PlasmaWave 5500-2 with an average CADR of 232 cfm. This air purifier can run as high as 4X ACH. So how much air Winix PlasmaWave 5500-2 clean in an hour?

Well, within 1 hour (or 60 minutes), Winix PlasmaWave 5500-2
can clean a capacity of: 232 x 60 = 13920 cfm.

With a room of typical 8 feet in ceiling height, you will have: 13920 (cfm)/8 (f) = 1740 (f².h)

Divide this value for the ACH, and you will have the answer: 1740 (f².h)/4 (h) = 435  f². Well, in the manual, Winix PlasmaWave 5500-2 is claimed to be effective in a room size of 360 sq ft.

After reading this article you should be able to know the importance of the ACH rating and CADR rating.

Read more articles about air purifiers:

Frequently Asked Questions About Air Purifiers
The Benefits of Air Purifiers
What is a HEPA Air Purifier? (What does a HEPA filter do?)
How Do I Choose an Air Purifier
How to Choose the Right Size for an Air Purifier