Minimum Efficiency Reporting Value (MERV) MERV is a measure used to describe the efficiency with which particulate filters remove particles of a specified size from an air stream.54 The higher the MERV designation, the better the efficiency of removal, particularly for smaller particles (Table 1). MERV levels 1 through 16 are determined using the ANSI/ASHRAE Standard 52.2-2007 test method by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).54 Standard 52.2-2007 does not address high efficiency particulate air (HEPA) filters or ultra low penetration air (ULPA) filters (MERV 17 – 20). HEPA/ULPA filters are assigned MERVs based on their performance in accordance with standards published by the Institute of Environmental Sciences and Technology (IEST).51 Table 1: MERV Parameters Composite Average Particle Size Removal Efficiency (%) in Size Range (ìm) - ANSI/ASHRAE Standard 52.2-2007  Contaminants Typically Controlled Typical Applications MERV 0.3–1.0 1.0–3.0 3.0–10.0 1 — — <20 Particles >10.0 ìm: pollens, dust mites, textile/carpet fibers Minimum filtration; residential buildings 2 — — <20 3 — — <20 4 — — <20 5 — — 20–35 Particles 3 - 10.0 ìm: mold, spores, cement dust  Most commercial and better residential buildings 6* — — 35–50 7 — — 50–70 8 — — >70 9 — <50 >85 Particles 1.0 - 3.0 ìm: Legionella, lead dust, coal dust, auto emmissons Superior residential and better commercial buildings 10 — 50–65 >85 11 — 65–80 >85 12 — >80 >90 13 <75 >90 >90 Particles 0.3 - 1.0 ìm: all bacteria, most tobacco smoke, droplet nuclei, most smoke Hospital inpatient and general surgery; superior commercial buildings 14 75–85 >90 >90 15 85–95 >90 >90 16 >95 >95 >95 IEST Standards 17  >99.97 on 0.30 ìm particles, IEST Type A  Particles <0.3 ìm (viruses, radon progeny, carbon dust) Cleanrooms and pharmaceutical manufacturing 18 >99.99 on 0.30 ìm particles, IEST Type C 19 >99.999 on 0.30 ìm particles, IEST Type D 20 >99.9999 on 0.10–0.20 ìm particles, IEST Type F   * Mimimum requirement under ASHRAE standard 62.1 (Ventilation for Acceptable Indoor Air Quality) Source: Adapted with permission from ANSI/ASHRAE Standard 52.2-2007: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineeers, Inc. 2007 © American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., www.ashrae.org

Last updated:June 9, 2008