"The original forced-air systems in buildings were furnaces, and rudimentary filters were used to prevent combustibles from entering the combustion area. As systems became more sophisticated and more expensive, and as delicate component pieces were introduced, filtration became increasingly important for protecting and extending the useful lives of components," said Doug Render, product manager for StrionAir.

StrionAir manufactures the GC Filter, which the company says combines elements of ionization, electrostatics, and mechanical filtration.

Render pointed out that this all changed following the energy crunch of the 1970s, when building envelopes were constructed tighter, resulting in higher concentrations of indoor pollutants. "Modern air filters must protect people as well as HVAC equipment," he said. "One aspect to improving IAQ is filtration efficiency."

Many consumers are becoming more and more educated about IAQ and the importance of air filtration, but consumers could use more guidance. And according to some manufacturers, contractors could use more information to guide their customers adequately.

"Proper air filter selection and promotion can be confusing, what with infomercials, outrageous claims, and many companies vying for business," said Charlie Seyffer, manager of technical services for Camfil Farr.

Seyffer believes that filter education for contractors has been limited. "Most service technicians, if they review their training manuals from school, will find only one to two pages on air filtration," he said. "With such limited training, it is almost impossible for a contractor to select the proper filter for a specific indoor air quality problem.

"At present, major filter suppliers pursue major end users directly, as they find this market easier to educate and hence generate income," he stated.

The MERV Movement

MERV ratings were put into place through American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 52.2. This standard was established in 1999, and was a way of establishing a minimum operating capacity for a filter. Through testing, a number or value is placed on a filter, which is meant to tell the contractor or consumer how the air filter will perform under minimum requirements against specific sized particles. Filters are ranked from a rating of MERV 1 up to a rating of MERV 16. Higher MERV ratings mean better filtration efficiency - the ability to screen out smaller particles more effectively. But there is more to selecting a filter than that. Contractors and consumers need to know what filters are effective for certain applications or certain IAQ goals.

Seyffer recommends that contractors research the contaminant that requires removal and use the MERV ratings to apply the proper filter for the job. For example, Seyffer explained that a pleated filter is not effective on tobacco smoke, while they are very effective at re-moving pollen, pet dander, etc.

"To remove tobacco smoke, a filter with a MERV of 13 or better is required," said Seyffer.

He added that there would most likely be significant system modification to accomplish the removal of tobacco smoke.

For the minimum efficiency level of filtration applied for any area of human occupancy, Seyffer said that a MERV-6 filter is needed. This is true for both resident and commercial applications.

ASHRAE has also set guidelines for specific commercial buildings. "The typical office environment should use a MERV of 7 to 11 or better," said Seyffer. "Consideration here includes extra contamination contributors, such as photocopies, computers, and additional human traffic."

ASHRAE also recommends museums include particulate filtration of MERV 13 or higher, plus a gaseous contaminate filter.

More Than MERV

According to John Paulos, Aprilaire's product manager for air cleaners, consumers need more than just a MERV rating.

"MERV ratings are attractive because they intend to provide a single number to use in comparing filters and air cleaners, and homeowners are increasingly looking at the MERV ratings to compare air cleaners," he said. "But MERV ratings really don't tell the whole story, and it is important to provide homeowners with enough data to make an informed decision."

For example, Paulos believes that MERV ratings don't give consumers a clear picture of how effective a filter will be.

"Most [consumers] are looking for a solution to a problem they already have," he said.

Paulos recommends that contractors find out what that problem is, whether it is dealing with allergies or household odors, and then address that issue with the appropriate filter.

Paulos indicated that the MERV rating alone ignores service life and performance over time. He suggests that contractors educate consumers on how often they will need to replace their filters. For example, a high-efficiency 1-inch-thick filter needs to be replaced every month. Paulos recommends that the contractor find out how often the consumer will want to change out their filters.

Render said that the issue is the same for commercial customers.

"Maintenance issues are always a consideration," he said. "Filters with short lives need to be replaced frequently. In many organizations, maintenance may not take place in a timely fashion, in which case the filters will be overloaded, causing problems to those associated with high static pressure filters. Alternatively, if maintenance is performed routinely, then the costs of short-lived filters may be excessive. So it is best to select filters that take a long time to reach their respective terminal pressure."

Contractors also need to educate consumers about filtering pathogens and particles.

"Particle accumulation upon air filters poses few concerns," said Render. "However, the buildup of pathogens can actually grow and breed upon air filters, emitting harmful toxins into the supply air."

Paulos said that contractors must remember that MERV ratings do not work for electronic air cleaners. "The test procedure specified by ASHRAE requires the use of a special dust that shorts the electronics in electronic air cleaners," he said. "So for electronic air cleaners, the test as designed doesn't provide an accurate reflection of the removal efficiency it is suppose to test."

Paulos said that with an Aprilaire electronic air cleaner, efficiency improves over time because of the media used, while with a plate-style electronic air cleaner, efficiency decreases as it loads.

Publication date: 05/10/2004