ATLANTA - A proposed addendum open for public comment is part of efforts to combine the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ (ASHRAE’s) two standards on air filter testing.

Combining Standards 52.1, Gravimetric and Dust Spot Procedures for Testing Air Cleaning Devices Used in General Ventilation for Removing Particulate Matter, and 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, would have several benefits for users, according to Monroe Britt and James Hanley, chairs of the Standard 52.1 and 52.2 committees.

“One benefit would be having a single ASHRAE test standard for determining the filtration efficiency of HVAC filters,” Hanley said. “This would reduce the number of tests needed on a filter. Currently, many filters are run twice, once for Standard 52.1 and once for Standard 52.2. It also would allow for one test rig to perform all the needed tests. Existing differences in the test rig requirements between the two standards make it difficult for one rig to serve both tests.”

Currently, the primary differences between the standards are:

• Standard 52.1 includes “dust spot efficiency,” while Standard 52.2 replaces the dust spot efficiency with efficiency measurements as a function of particle size.

• Standard 52.1 has an emphasis on average efficiency of the filter, while Standard 52.2 has an emphasis on the minimum efficiency.

• Standard 52.1 includes weight arrestance that is currently not included in Standard 52.2. Weight arrestance is mainly applicable to relatively low efficiency HVAC filters.

• Standard 52.1 allows flow rate and final pressure drop to be selected by the person requesting the test whereas Standard 52.2 has prescribed flow rate and final pressure drop criteria.

• Standard 52.2 includes the Minimum Efficiency Reporting Value (MERV).

• Standard 52.2 includes a “conditioning step” to better reflect changes in efficiency that filters can undergo in actual use.

Proposed addendum b would incorporate the Standard 52.1 sections on weight arrestance and dust-holding capacity into Standard 52.2 and deletes some references to Standard 52.1 that occur in Standard 52.2. The addendum is open for public review until April 30. Also open for review is proposed addendum a, which revises the first dust-loading step, also known as the conditioning step, in Standard 52.2.

On a parallel path, the 52.1 committee is working to revise the 52.1 standard to remove the dust spot efficiency test requirements.

“Whereas, this test method has served the air filter industry well for several decades, the particle size efficiency technology presented in 52.2 provides more direct and useful data than the dust spot efficiency data,” Britt said.

This revised standard 52.1 will be submitted for public review in the fall of 2007. When the revised standard is approved, the 52.1 standard will become redundant and will no longer be needed. At that time, ASHRAE will take steps to undergo a public review process to withdraw Standard 52.1 so that Standard 52.2 will become the sole ASHRAE standard on filtration efficiency.

Proposed addenda to ASHRAE standards are available during public review periods. To read the addenda or to comment, visit

Publication date:04/16/2007