Learn About the Air Purifier CADR Ratings Scale
CADR is one of those technical terms that is not easily understood. It stands for Clean Air Delivery Rate.
In short, it 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 it’s hit or miss whether an air cleaner will have a CADR number.
There are 3 sizes of particles 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 measured 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.
CADR is measured in 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 that are tested. 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 is finer 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 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 mainly used to determine 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.
Air Filters and CADR
A criticism that some brands 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 pounds carbon filter will do much better. However the air cleaner with this type of filter will have a lower CADR value.
A similar criticism applies to HEPA-type filters. Say, a HEPA-type filter can remove 90% of airborne particles while a true HEPA filter is at 99.97%. If each air filtration system can move 100 cfm (cubic feet per minute) through the air purifier filters, then the HEPA-type unit will have a CADR of 90 and the true HEPA system will have a CADR of 99.97.
So, it seems the HEPA air purifier is better. But this isn’t what happens. The issue is with a higher efficiency filter, especially at the top end of the MERV ratings scale, the air flow resistance increases a lot.
Suppose the HEPA-type and HEPA air cleaner from our example have the same fan and the air flow resistance is 30% higher with the HEPA filter.
Then the CADR will be the same 80 for the HEPA-type and 70 for the true HEPA.
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 in our testing is that many models don’t use a lot of carbon for this reason.
Given these limitations we do our testing a little differently.
Yes, the air flow through the air purifier filters is important since you need to move the air. However, we also recognize that you need to have the smallest particles removed. So, in our testing and ratings we value the use of higher efficiency filters.
We also value the use of additional activated carbon if you need a smoke air purifier. If you have a larger sized room or want the best in smoke removal we recently added a page on commercial air purifiers. While this may sound industrial these are really high end systems that are commonly used in homes.
Some Additional Things to Consider about CADR
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.
Products 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.
How We Rate Air Purifiers
Our approach to rating air purifiers includes key aspects of the CADR. By this, I mean we measure the filtered air flow.
But we do it in a different way. We separate air flow and filter efficiency into separate scores. The air flow gives an indication for how well the air purifier will circulate the air in a room.
The filter efficiency measures how well the air purifier removes the smallest particles. Those that are most important to remove from the air if you have allergies, asthma or other respiratory issues.
A higher efficient filter will be penalized by the CADR rating since it has more air resistance.
By splitting the two scores out we are able to let you see how each air purifier does with both.
In addition, we also give a rating for ease of use. Yes, this can be subjective. And maybe you don’t care about this. If so, then please ignore it.
We also give a rating for customer feedback. We read hundreds of customer reviews and boil down their feedback into a summary.
Summary
In this article we introduce you to the CADR ratings, short for Clean Air Delivery Rate. This is a voluntary program that is administered by AHAM (Association of Home Appliance Manufacturers). This is the industry standard however only about half of the air purifier brands on the market seem to participate.
The ratings scale is made up of 3 parts: smoke, dust and pollen. Each represents a different airborne particle size. The CADR is a reflection of the clean air flow through the air purifier filters.
The benefits and drawbacks to the CADR system are presented.
We conclude with an explanation for how we rate air purifiers and attempt to overcome some of the shortcomings of the CADR rating system.
