The Association of Home Appliance Manufacturers (AHAM), which tests, certifies, and publishes CADR's, is an industry lobbying group of home appliance manufacturers.
This trade association represents manufacturers of major home appliances, portable and floor care appliances, and suppliers.
The key to understanding the CADR rating lies not in a technical explanation, but in marketing territory.
Note that many, but not all, mass market air purifiers are built by appliance makers.
Attempts to build a rival air purifier trade association were basically preempted by AHAM's land grab.
The International Association of Air Cleaner Manufacturers exists, but with a lower profile than the ubiquitous AHAM.
In the 1980's AHAM established a rating system and certification program for portable room air cleaners.
They call it Clean Air Delivery Rate.
Participants are required to display the AHAM endorsement sticker on packaging of certified room air cleaners.
According to AHAM, about 50% of consumers are confused and reluctant to purchase air cleaners after shopping.
The delivery rating was designed to "help" consumers evaluate air cleaner choices.
I agree that objective standards were, and still are, needed.
It is difficult to review a flawed system which stands between consumers and anarchy.
In fact, some marketers who have not submitted their products to AHAM's tests will claim to have "great CADRs" or even cite specific falsified ratings.
So while I criticize CADRs, and heartily endorse many products which are not certified, I warn buyers to avoid all products from vendors which falsely pretend to be AHAM certified.
But isn't CADR a lot like the fox running the chicken coop?
Ads everywhere claim that the AHAM delivery rate is the central piece of information consumers should use to evaluate air cleaning performance.
Even I emphasize it in product reviews, especially for less expensive products intended primarily for particle removal.
"Just look for the AHAM seal"
AHAM uses an independent lab to verify clean air exhaust rates submitted by manufacturers for given air cleaner models.
Clean air delivery is the volume of air that a specific model air purifier cleanses of a specific pollutant in cubic feet per minute.
Air cleaners are rated for effectiveness at removing particulates - dust, pollen and smoke.
CADR tests last a very short 20 minutes.
Tested units are random-selected brand-new from the manufacturer's regular production.
The lab does a 48 hour run-in without filters prior to verification tests.
For air delivery rate verification tests, a closed chamber is filled with dirty air to clean; particles ranging in size from .01 microns to 11 microns, representing tobacco smoke, mulberry pollen, or Arizona road dust.
When particulate matter reaches a prescribed level, the air purifier being tested is turned on.
Particle concentrations are measured at 2 minute intervals for 20 minutes and the particle removal rate is determined for each test product and contaminant type.
CADR is the airflow in cubic feet per minute (cfm) multiplied by the efficiency (percentage) of particle removal.
AHAM's air delivery rates for dust go from 10 to 400, tobacco smoke from 10 to 450, and pollen 25 to 450.
The AHAM directory is published twice a year, in January and July.
The EPA and the FTC have reviewed the testing process.
The AHAM spec is accepted by the American National Standards Institute (ANSI).
Consumer Reports has embraced the CADR system, and considers scores above 350 excellent and below 100 poor, seldom recommending any purifier with less than 150.
During the legal feud between Sharper Image and Consumer Reports, evidence of “criticism” of the AHAM clean air rate was presented by the Breeze's counsel.
A federal court reviewed those arguments and concluded CR was correct in using CADR-like tests to rate the nearly cadr-less Ionic Breeze.
The court could find no expert to suggest that CADRs are scientifically flawed, or that testing was biased or irregular.
In fact, a reading of AHAM's requirements suggests they, and the outside lab, are very disciplined.
That sounds good, so what could be wrong with the AHAM delivery rate for clean air?
So What's Wrong With CADR?
It's what CADRs don't say that makes them so useful to builders of mass market air cleaners.
Here are my criticisms of the AHAM air purifier delivery rate tests.
Clean air delivery rate does not effectively measure removal of some critical health hazards we buy air purifiers to collect!
While AHAM has modified its tests to include finer particles, it still employs only a very broad efficiency range to adjust CADR figures.
This favors lower quality units.
Quality air purifiers retain a high percentage of particles at .1 micron.
Nine microns, at one time the only particulate tested, is 90 times as large.
Since 90% of all particles are below 0.3 microns, and the finest fragments are the most damaging to health, what is important is the air purifier's efficiency at retaining sub-micron particles in the .5 micron and below range.
CADR still directs buyer attention away from this critical data.
The naked human eye can barely see particles 35 microns in size, just above the upper range of the specification (11 microns).
Secondly, CADR is irrelevant to chemical contamination of all kinds.
It simply ignores Volatile Organic Chemical (VOC) and odor pollutants.
AHAM chose to base its ratings on particle filtration alone.
VOC's and odors are molecular sized, and zip right through most high CADR air cleaners.
High quality air purifiers with real carbon filtration and tight gasketed filters are at a big disadvantage in the clean air delivery game. Quality machines operate at higher internal pressures, CADR favors a strong fan generating high throughput at low pressure.
With real carbon filters, photocatalytic oxidation, and ultraviolet light systems, faster is not necessarily better.
These systems require from .1 to .5 seconds dwell time for UV exposure, carbon adsorption, or complete contact with oxidative catalyst surface, to be fully effective.
Real air purifiers, (IQAirs, Austin Airs, NQ clarifiers, and other premium units), with tight filter stacks and heavy carbon which do more air cleaning, will not rate well in delivery of "clean" air.
IQAir's prefilter is 55% efficient at 0.3 microns, how could CADRs measure this?
Third, the test is very short, obscuring long term performance shortcomings of electrostatic precipitators and inferior HEPA models, both of which experience efficiency declines with age and quality of maintenance.
Top CADR performers include Blueair 603, electrostatic models designed specifically to do well on CADR.
Fourth, CADR is measured on noisy high speed, and may not accurately assess low speed or quiet speed performance.
No assessment is made of automatic controls, quiet operation, and user interface, considered critical here.
Few consumers will tolerate the interference of loud air cleaners, yet the tests are done using continuous high speed.
Of course AHAM itself makes no assertions of performance beyond what is actually measured, that is left to the discretion of individual marketer.
AHAM certification is voluntary, and while the number is growing, only about 42 companies have joined up.
The list is populated mostly by appliance firms building air cleaners as a sideline.
Names that fit that description are Honeywell, GE, Hunter, Holmes, Whirlpool, Friedrich, Sharp, and Kenmore.
Builders have to pay a fee as high as $10,000 to have their products certified.
Most quality brands have not joined, including IQAir, Austin Air, Clarifier, and Aller Air.
Blueair, which always scores well, features clean air delivery heavily in their advertising.
Builders displaying the AHAM seal pay a commission for every box they sell.
Who really pays for this form of advertising?
While there are European standards, no other nationally recognized test has emerged that can supplant AHAM's.
A new design which addresses the above issues, and is politically acceptable to all parties, is unlikely.
For lack of valid alternatives, Air-Purifier-Power will consider CADR as one of many factors when evaluating lower priced units without VOC gas capability.
The cheaper the purifier, the more important the AHAM air delivery rate becomes, relative only to other units in it's price class.
For those concerned about health, the clean air delivery rate should not be considered a primary standard to measure air purifier effectiveness.