(Air quality can be measured with hand held instruments like this one)
Consumers who have decided to take the step of purchasing an air purifier are faced with a wide range of choices. How are they to know which air purifier is the best choice? A few different ways to measure purifiers' effectiveness have cropped up. This article will discuss the different ways that air purifiers are ranked.
The National Air Filtration Association, which describes itself as "a group of over 600 air filter distributors, manufacturers and engineers," uses this ranking system, devised by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) along with the American National Standards Institute (ANSI). Here is how the ANSI/ASHRAE test is performed:
The ANSI/ASHRAE Standard is a reasonably good way to determine the quality of large air purifiers. According to the Environmental Protection Agency, "Medium efficiency filters with a MERV of 5 to 13 are reasonably efficient at removing small to large airborne particles." A higher MERV than that range can only be achieved by air purification systems that could not easily be installed in the typical residence.
This method has been developed by the Association of Home Appliance Manufacturers (ANSI). The goal of this method, in the words of AHAM, is to measure the effectiveness of "portable household electric room air cleaners ... regardless of the particle removal technology utilized." The ANSI method works in the following manner:
The AHAM tests are useful in comparing different portable air cleaners with CADR ratings to one another. The CADR rating is used by two important organizations outside of AHAM: the EPA and Consumers Union, publisher of Consumer Affairs magazine, which independently reviews air purifiers. In the feud between Consumers Union and The Sharper Image over the Ionic Breeze, the courts rejected Sharper Image's claim that CADR was a poor way of measuring the efficacy of air cleaners.
However, not everyone is so enthused about the use of AHAM-ANSI. The fact that AHAM is a trade association of appliance manufacturers raises warning bells, since it means that the makers of the products are testing themselves rather than using independent standards. Ed Sherbenou, operator of the website "Air Purifier Power," has decidedly mixed feelings on CADR rankings. While acknowledging their usefulness, he also raises some objections:
Ultimately Sherbenou suggests that buyers consider CADR only as one factor among others.
Beyond these objections, it must also be noted that CADR ratings are not useful for larger air purification systems that target the whole home, as the AHAM-ANSI test was designed specifically with portable systems in mind.
Particle counters are relatively small devices that are used to measure the density of particles in a room, as well as their size. There is less to say about these, as they are a tool rather than an organized method of rating purifiers. They work by emitting a laser, and the counter detects and categorizes the particles that pass through it. They are an accurate way, when used systematically, of measuring a purifier's impact on a room's air quality.
No method of measuring the performance of an air cleaner is perfect. Larger systems have the basically reliable ASHRAE Standard, but these are not useful for portable models. The AHAM's CADR rating can be useful in evaluating a purifier, but it can also be misleading and biased. Therefore, potential buyers should look beyond any rating given to a device and consider other things as well; for instance, finding out whether the purifier is effective against very particles and gasses that cause health problems.