Indoor Air Resources

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It's Time You Learned the Unfiltered Truth

February 2015

By: Kevin Morrow, Business Development Manager, Kimberly-Clark Professional Partnership Products  |   02.12.15

Are you confused about the benefits of electret-treated filters? Are you concerned they may decline in efficiency based on results of the optional MERV-A test (Appendix J) in the ASHRAE 52.2 Test Standard? Some manufacturers are using that optional test to divert attention away from the real-world performance advantages of electret treated media. 

What they don’t tell you is that filters using electret-treated media are much better at capturing the smallest airborne particles (E1) that can cause health and productivity problems like asthma and allergies in building occupants. 

Healthier Buildings, Healthier People

Recent testing showed that MERV 8 filters using electret-charged media perform on average 20 percentage points higher in E1 and E2 efficiency than mechanical filters on the market today. These results closely match previous test data comparing mechanical and electret-treated media. 


Filter A

Filter B

Filter C

Media Type




Advertised MERV




Tested MERV




E1 Efficiency




E2 Efficiency




E3 Efficiency




Initial Pressure Drop (WG)




Testing conducted in June 2014 by LMS Technologies, Inc. Data are an average of two initial 52.2 tests and one full 52.2 test per filter model. 

Better Efficiency

Electret-treated filters achieve both high initial efficiency (mostly due to the charge) and high sustained efficiency (mostly due to the structure). In addition, this efficiency does not decline during long-term storage, even at high humidity conditions. 

In addition, electret-treated filters typically deliver lower airflow resistance than mechanical-only filters, which translates directly to reduction in energy consumption and costs, as well as reduced greenhouse gas generation. 

MERV-A Exposed

Testing for MERV-A results under Appendix J of the ASHRAE 52.2 Standard subjects filters to extreme loads of very fine particles—many times what the filter would be exposed to over its actual life. It represents a worst-case scenario that is likely to never happen. 

Moreover, these same conditioning techniques have been shown to decrease the filtration efficiency of certain mechanical-only filters as well, and it’s not uncommon to find lab-to-lab variances in the test procedure, meaning that the techniques used to condition the filters are not repeatable. 

While the optional Appendix J test method may be conducted at the filter manufacturer’s discretion, only the standard, ANSI-certified ASHRAE 52.2 test method can indicate the filter’s true performance. So be sure to examine the filter’s efficiency in all particle size ranges: E1 (very fine particles in the 0.3 to 1.0 micron range), E2 (fine particles in the 1.0 to 3.0 micron range), and E3 (coarse particles in the 3.0 to 10.0 micron range). That will tell you the ability of the filter to capture the smallest and most toxic particles—the ones most likely to travel to the deepest part of the lungs, where they can cause a variety of health problems. 

Look Beyond MERV

Many filters have low E1 and E2 efficiencies. In fact, under ASHRAE 52.2, filters in the MERV 1-2 range aren’t even measured for E1 efficiencies, and filters in the MERV 1-8 range aren’t measured for E2 efficiencies. And if you specify a filter based on its MERV-A results, you could end up with a filter that has inferior E1 particle capture to a MERV 8 electret-treated filter.


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