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Air Filter & Air Filtration Technology Air Filter MERV Ratings

by Richard Carrow (Danforth Air Filtration & Air Purification, Buffalo, NY)

Air Filter MERV or Minimum Efficiency Reporting Value is an expression of the filtering efficiency of an air filter that has been evaluated using the ANSI/ASHRAE Standard 52.2 Test Procedure. An air filter’s performance is determined by comparing airborne particle counts upstream and downstream of the air filter (or other air cleaning device) under test

Danforth Air Filtration & Air Purification and Danforth Indoor Air Quality Division work together to maintain Your HVAC / Air Filters / Air Cleaners / Air Purifiers, and coordinate required periodic testing and preventive maintenance on all types of air filtration & air purification systems in New York State

Air Filter MERV Determination

The MERV rating of an air filter or other air cleaning device is ascertained by using the ANSI/ASHRAE Standard 52.2 Test Procedure: Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size.

The process involves injection of an aerosol challenge (containing particles in 12 different known size ranges) into an air stream that passes through the air filter under test. Airborne particle counts are then recorded for each particle size, both upstream and downstream of the air filter in order to determine how efficiently the air filter filters out the particles.

This test is repeated 6 times for each particle size, with the results stated as a filtration efficiency ratio of the downstream to upstream particle count. The lowest values over the six test cycles are then used to determine the Composite Minimum Efficiency Curve for that air filter.

Once these values are compiled, the 12 size ranges are distributed into 3 larger groups called E-1, E-2 and E-3. Averaging the Composite Minimum Efficiency for each group will calculate the average Particle Size Efficiency (PSE) of the air filter, and the resulting percentages are used to determine the MERV rating.

The MERV rating is a number from 1-16, stated along with air velocity at which the test was performed, to simplify the evaluation of an air filter using this test method.
ANSI/ASHRAE Standard 52.2 Updates - Adendum B (On Arrestance & Dust Holding Capacity), and Appendix J (On MERV-A Ratings)

Higher MERV Rating Equates To Higher Air Filtration Efficiency

Summary

Air Filter MERV or Minimum Efficiency Reporting Value is an expression of the filtering efficiency of an air filter that has been evaluated using the ASHRAE Standard 52.2 Test Procedure. An air filter’s performance is determined by comparing airborne particle counts upstream and downstream of the air filter (or other air cleaning device) under test.

Typical
AirFilter
Type
Disposable Panel Filters, Fiberglass & Synthetic Filters, Permanent Self Cleaning Filters, Electrostatic Filters, Washable Metal Foam Filters Pleated Air Filters,
Extended Surface Air Filters,
Media Panel Filters
Non-Supported Bag Filters,
Rigid Box Filters,
Rigid Cell / Cartridge Filters
Non-Supported Bag Filters,
Rigid Box Filters,
Rigid Cell / Cartridge Filters
MERV 13 Pleats
HEPA Filters,
ULPA Filters,
SULPA Filters
MERV Std. 52.2 1-4 5-8 9-12 13-16 17-20
Average Dust Spot Efficiency <20 % <20 to 35% 40 to 75% 80 to 95%+ 99.97%
99.99%
99.999%
Average Arrestance ASHRAE Std. 52.1 60 to 80% 80 to 95% >95 to 98% 98 to 99% N/A
Particle Size Ranges >10.0 microns 3.0-10.0 microns 1.0-3.0 microns 0.30-1.0 microns <0.30 microns
Typical Air Filter Applications Residential,
Light Commercial,
Equipment Protection
Industrial Workplace,
Commercial,
Paint Booths
Industrial Workplace,
High End Commercial Buildings
Smoke Removal,
General Surgery,
Hospitals and Health Care
Clean Rooms,
High Risk Surgery,
Hazardous Materials

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