CADR Ratings Scale

CADR is a technical term that is not easily understood. It stands for Clean Air Delivery Rate.

The CADR ratings scale is a metric that is the volume of filtered air.

Keep reading and I will explain what this means and what this is important in choosing a good CADR air purifier.

How It Works

CADR comes from AHAM (Association of Home Appliance Manufacturers). This is a way for you to compare the amount of clean air from air purifiers. The AHAM CADR is a voluntary program so not all air cleaners will have a CADR number.

Three sizes of particles are measured. They each give an indication of the air purifier’s ability to remove the smaller particles (smoke) up to larger sized particles (pollen).

Smoke CADR (0.09 – 1 micron)
Dust CADR (0.5 – 3 microns)
Pollen CADR (5 – 11 microns)
There are two factors that influence the CADR ratings scale. They are the filter efficiency and the air flow through the filters.

Taken together they give an indication for how much filtered air you will get from the air purification system.

The CADR represents the amount of clean air coming out of the air purifier on the highest fan speed. It is only tested on the highest fan speed. If you run the air cleaner on a lower fan speed then the CADR will be lower since the fan airflow is less.

The CADR unit of measure is cfm or cubic feet per minute in the US.

For example, if the air purifier produces 100 cfm and the filter removes 90% of particles (efficiency) then the CADR for the air purifier will be 90. 100 times 90%.

In Asia and Europe the CADR is given in cubic meters per hour.

Clean Air Delivery Rate to Room Size

You may be wondering how to convert the CADR to something practical like the size of your room.

According to AHAM, they suggest you take the CADR rating and multiply this by 1.55 to get the room size. This is based on a ceiling height of 8 ft.

For example, a 100 CADR air cleaner will then clean a room size of 155 sq ft.

To go the other way, that is to know your room size and to find the right CADR you would then divide your room square footage by 1.55.

Say your room is 250 sq ft. Divide this by 1.55 and you get 161. This means you will want a room air cleaner with a CADR of 160 or higher.

AHAM recommends you use the smoke CADR to calculate the room square footage. Given this is the smallest particles sizes they measure it seems like the most difficult to achieve a high score.

CADR Particle Size

As listed above there are three CADR numbers. What you will often see is one CADR rating and in many cases this is an average of the three ratings.

While the names are smoke, dust and pollen this is to only represent the relative airborne particle sizes. For example, dust particles can range from fine dust that is smaller than the range of the CADR scale.

The pollen CADR represents the largest airborne particles. This represents things like pet dander, pet hair, dust mites, and larger sized mold spores, pollen and dust.

The dust CADR represent smaller sized pet dander and dust.

If you are looking for tobacco smoke removal it’s fair to say you will want to remove both the smoke particles and the tobacco smoke odors. The smoke CADR is a bit of a misnomer in that is only measures particulate matter. It does not in any way reflect what to expect in odor removal. Though, given it reflects the smallest sized particles that they test, it is the best number to use for smoke or air pollution removal.

Currently, the AHAM CADR (Clean Air Delivery Rate) has no air quality testing for gas or odor removal. So, it does not show results for volatile organic compounds or any other gas.

CADR Scale

The CADR rating scale goes up to 400-450 depending on the particle size measured. Dust CADR can be as high as 400 and the pollen CADR and smoke CADR can be as high as 450.

The CADR gives a relative performance indication. It is used to determine the room size coverage of the air purifier.

In addition, the Energy Star program for air purifiers is based in part on the Dust CADR. To achieve the Energy Star designation the air purifier must have a dust CADR rating that is at least 2 times the power on the highest fan speed.

So, if the air purifiers draws 100 watts on the high fan speed it must have a dust CADR of at least 200.

CADR Criticisms

A criticism that some have with the Clean Air Delivery Rate is that it penalizes the use of higher efficiency HEPA filters and activated carbon.

The issue is that with a genuine true HEPA filter or better the air flow resistance is higher. The same is true with a lot of activated carbon. If you have a foam carbon pre-filter with large openings it will have much less air flow resistance than a 5 pound thick layer of granular activated carbon.

From an air cleaning ability to remove smoke and odors the 5 pound carbon filter will do much better. However the air cleaner with this type of filter will have a lower CADR value.

This air flow resistance can be even higher with the use of a lot of activated carbon. It’s difficult to move the air through a lot of carbon. What we see is that many models don’t use a lot of carbon for this reason.

Additional Considerations

It only reflects the clean air on the highest fan speed. There are no measurements at the lower fan speeds. If you run the air cleaner on a lower fan speed your room coverage will be less.

Does not consider the air purifier noise level.

It does not consider ozone.

Features like a UV-C light have no impact either way on the CADR rating. It could impact the Energy Star rating somewhat since the UV light will add some additional power that is drawn by the air cleaner.

Does not represent air filter performance over time. It’s a measurement for what to expect with respect to the maximum amount of filtered air from a new air cleaner.

Relevant only to room air cleaners. There is on CADR type standard for whole house air cleaners.

The smoke CADR rating only reflects the removal of smaller sized airborne particulate (like tobacco smoke particles). It does not indicate whether a particular home air cleaner is effective for cigarette smoke removal.

Air purifiers that use electronic filtering like negative ionization may get an artificial boost in performance. Some reports state that a negative ion charge can cause airborne particles like mold spores to stick together and then adhere to the test chamber wall. This will show as being filtered from the air in the CADR test when in reality is has not been filtered.