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Protecting Building Occupants from Exposure to Biological Threats

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 (μm) - ANSI/ASHRAE Standard 52.2-2007 Contaminants Typically ControlledTypical Applications
1<20Particles >10.0 μm: pollens, dust mites, textile/carpet fibersMinimum filtration; residential buildings
520–35Particles 3 - 10.0 μm: mold, spores, cement dust Most commercial and better residential buildings
9<50>85Particles 1.0 - 3.0 μm: Legionella, lead dust, coal dust, auto emissionsSuperior residential and
better commercial buildings
13<75>90>90Particles 0.3 - 1.0 μm: all bacteria, most tobacco smoke, droplet nuclei, most smokeHospital inpatient and general surgery; superior commercial buildings

IEST Standards

17 >99.97 on 0.30 μm particles, IEST Type A Particles <0.3 μm (viruses, radon progeny, carbon dust)Cleanrooms and pharmaceutical manufacturing
18>99.99 on 0.30 μm particles, IEST Type C
19>99.999 on 0.30 μm particles, IEST Type D
20>99.9999 on 0.10–0.20 μm particles, IEST Type F  

* Minimum 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 Engineers, Inc. 2007 © American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.,

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*Note: The information that appears on the pages collectively known as "Protecting Building Occupants" was up-to-date and accurate when published in 2008; the materials have not been updated since original publication. Please be sure to check current resources for the most up-to-date information on this topic.



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