I have had many calls and emails asking me about CADR Air Purifier Ratings. What it means, and whether it is a good way to measure air purifier quality. Especially when they find companies that do not use it.
Here is my experience…
What are CADR Ratings
Would you like a reliable way to compare one air purifier to another? The AHAM CADR rating is one method used by some air purifier manufacturers to promote the value of their products.
But what is this CADR air purifier rating? Is it a reliable means to compare air purifiers? If so, why do so many top-quality air purifier manufacturers not bother to get their units rated?
CADR, short for Clean Air Delivery Rate. Developed by the Association of Home Appliance Manufacturers (AHAM) as a means of providing air purifier ratings to consumers.
Basically, CADR is a measure of an air purifier’s ability to produce pollutant-free air.
The CADR measures a certain number of cubic feet per minute. That is, the CADR essentially states the volume of clean air a portable air cleaner can produce at one time. For example, suppose a particular model has a CADR of 250 for dust. That means the unit can reduce dust particle concentration equivalent to adding 250 cubic feet per minute of dust-free air.
The manufacturers in this association are the very ones who determine what to test, how it will test, and what is a good performance. They decide by a negotiated mutual agreement among the associated manufacturers.
Obviously, the air purifier manufacturers have a vested interest in creating a test their products will perform well in. Unfortunately, this conflict of interest has created a test with severe limitations.
Many air purifier companies actively market their cleaners based predominately on this rating which stands for “Clean Air Delivery Rate”. It is a measure of air flow, not air purity. Therefore, other companies will skip this CADR Air Purifier Ratings altogether. Because it does not address some technologies critical to cleaning and purifying the air. CADR is associated with air flow alone, make its numbers, at best, Irrelevant and at worse, Misleading.
Why is it misleading to compare air purifiers by CADR numbers?
Most units only state three CADR numbers: one for smoke, another for dust, and a final one for pollen, which are the largest of all particles.
The number means much the same thing in each case. It still refers to the ability to reduce that material’s concentration by a certain amount in each time. It’s just that virtually all units can do that differently for the different kinds of home air pollutant. So the manufacturers state different ratings for each category. There are lots of reasons for that: particle size and weight, filter efficiency which differs from one type to another, and more.
One of the reasons home air purifier makers go to the trouble of measuring and reporting those three different numbers. Is that they are (almost) all members of the AHAM, the Association of Home Appliance Manufacturers.
That organization certifies that the numbers that air purifier makers report are accurate and honest. They use an independent, 3rd party lab to test the devices and verify the numbers reported.
Of course, “honest” is a little bit of a relative term here. No major manufacturer tries to deliberately misreport their numbers. That would threaten their membership in the AHAM and result in bad publicity, something none of them wants. But there are various ways they can report those numbers that can differ from one device to the next.
How to Easily Manipulate CARD Numbers
The fact is, if a manufacturer wanted to market their purifier just according to the CADR numbers. They can simply ‘beef up’ the fan speed, eliminate certain technologies and just manufacture the same limited filtration systems most companies use. For example, if you pull air too quickly through the unit to artificially inflate your CADR numbers. Any UV technology that protects you and your family from harmful germs and viruses. That traditional air purifiers miss, might negate any effects of killing germs and viruses.
CADR Air Purifier Ratings Do Not Factor Germs, Bacteria, Mold, Mildew, Fumes, Odors, etc.
The CADR is basically only a measure of how rapidly air circulates through a given air filtering device. While this figure is perhaps relevant for most filtration-only devices that attempt to clean air using only one or two types of filters. It is meaningless because filtration is simply one single aspect. The fact is that the CADR number tells you nothing about how well, or even “IF”, an air purifier filters germs, bacteria, viruses and other harmful biological agents. Neither does it assess how well the unit clears chemical fumes and odors.
The easiest way to think of it is that, even though everyone in the industry refers to their products as an air “purifier”. The fact is that most competing products out there are simply air “filters” that do not use anywhere near the number of additional “purification” technologies available, e.g., UV light, TiO2, activated charcoal, negative ionization, etc.
Ways of Reporting CADR
Two different home air purifier makers may have units with identical CADR numbers but still be quite different in their ultimate effects.
The key to using CADR numbers to compare models accurately lies in two things: (1) take them as approximate, (2) look closely at what is behind them. The first is obvious, but what does (2) mean?
Simple, just get the context around that number. Look for the number of air exchanges per hour, and the specific room characteristics assumed by the CADR. The AHAM gives manufacturers a little leeway here.
A stated CADR references a ‘standard’ room. Ensure that your room is ‘standard’. That is, the standard used for CADR’s assumes an 8-foot-high ceiling because the ordinary home has (or had for many years in the U.S. after WWII) a ceiling that high.
As the years have rolled on, more and more home designs deviated from that, so adjust accordingly. If your home has a cathedral ceiling, an open area that leads up to a second floor, or other deviation from ‘the norm’ look for a home air purifier with a larger number to compensate.
In brief, don’t assume that because your floor area square footage is the same or even smaller. Than what the model specifies that the device will purify your room air totally. The device operates, after all, on the total volume, not just the air from your head on down.
It’s a good idea to follow the AHAM’s “2/3 Rule” but modified. What’s that?
The (Modified) 2/3 Rule
Suppose you have a room measuring 10′ x 12′ (120 square feet) whose air you want to purify and keep smoke-free. You should look for a home air purifier with a Smoke CADR number of at least 80. (120 x 2/3 = 80).
The CADR test on the air purifier only use the highest setting. Since your home unit will typically run at the middle speed/power most of the time. The CADR obtained by the 2/3 Rule is the bare minimum and you should add about 30% to get a ‘floor’ on the CADR number.
So, start with 120 x 2/3 (the 2/3 rule) = 80. ADD 1/3 to that, so: 80 + (80 x 1/3) = 107 (approx).
That calculation assumes an 8-foot ceiling. So naturally if you have one that’s higher or not flat, open to another story, etc. multiply accordingly. It would be too complicated to detail here what is “accordingly” for the general case, so just approximate your situation.
For example, if you have a 12-foot sloping ceiling, add about another 30% to the number. So, for this case, that number becomes: 80 + (80 x 1/3) + (80 x 1/3) = 133 (approx).
CADR Helpful but Not the Only Factor to Consider
CADR numbers, helpful as they are as a starting point. They are not the only important feature for ensuring a good air purifier model as the ratings don’t capture some especially useful information.
For example, because the AHAM tests are short they don’t tell you how the air purifier will perform over the long haul. They also don’t encapsulate how well the air cleaner captures small particles. Which are often the most damaging to health nor do they tell you how well a model removes VOCs (Volatile Organic Compounds), which can be unpleasant or even unhealthy.
So, the moral is: use the CADR as a starting point but look also to other features of any home air purifier you’re considering before you make a final choice.
To start on the process the AHAM maintains a searchable Directory of Certified Room Air Cleaners.
Include link – https://www.ahamdir.com/room-air-cleaners/
The size of these pollutants is quite large in comparison with other particles found in the air. Over 90% of all airborne particles in our homes and offices are smaller and include viruses, bacteria and mold.
CADR air purifier comparisons provide no indication of a filters efficiency at removing these smallest of all particles. These are the the ones that purifiers are generally the least efficient at removing. This test also does not measure gas and odor reduction. Since most people buy air cleaners for these purposes, this standard is of no real value to consumers.
Longer-term tests clearly show that collector plate loading by contaminants can reduce efficiency to less than 20%. This can have a severe impact on Clean Air Delivery Rate that would not show up in the CADR testing. Failure to provide consumers with this critical information prevents them from understanding how important it is to follow use and care directions routinely.
The top four reasons the AHAM CADR rating is unreliable
- The rating test performed by CADR is not a strict, definitive test. It fails to address the majority of lung damaging airborne particles.
- The test just measures the elimination of the particles. Even ionizers rate well. The well-documented ineffective filtration and dangers of ionizer air purifiers is a good indication that this test is questionable.
- The test does not measure the performance of the elimination of gas and odors. Although many people buy air cleaners for this purpose.
- The major downfall with the test is that it does not measure long-term performance. The values in CADR air purifier comparisons represent performance during the first 72 hours of use. Air cleaning system generally run for 5000 hours before you replace the filter. The performance over this span will often be drastically lower and depends to a significant degree on the construction of the air cleaner and the air cleaning technology.
Based on these concerns CADR air purifier comparisons are questionable and fail to really serve the best interests of consumers. The manufacturers of the world’s best air purifiers universally ignore this test. Submitting to it would seem to grant it an air of credibility while failing to really prove the superiority of the air purifiers they have to offer you.
A better standard than the AHAM CADR rating is available
A superior testing method to the AHAM CADR rating went into effect in 2000. This determines HEPA efficiencies in the smallest of particles over extended use. It determines air purifier effectiveness under a worst-case scenario.
It is known as EN1822 (European Norm 1822).
Link – https://www.en-standard.eu/set-en-1822-and-en-iso-29463-standards-for-heigh-efficiency-air-filters-epa-hepa-and-ulpa/
The EN 1822 standard tests air purifier effectiveness over a broad range of particle sizes. This determines the particle size the filter is the worst at removing, known as the Most Penetrating Particle Size (MPPS for short). These particles then test the filters efficiency at air speeds that reflect actual use conditions.
Since this gives the absolute worst-case scenario performance measure, there is assurance of real-world performance in their own homes.
CADR will give you some idea of how the air flows across your HEPA filter, but that is about it. It will not give you any idea of the purifier’s effectiveness in eliminating odor, gas, viruses, bacteria, etc.