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All About Air Filter MERV Ratings

The Minimum Efficiency Reporting Value (MERV) represents the filtering efficiency of an air filter as set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). The metric is evaluated using the ANSI/ASHRAE Standard 52.2 Test Procedure, which counts airborne particles both upstream and downstream of the air filter. The standard clearly outlines the testing protocol that needs to be followed to ensure reliable and consistent test results of air filter performance.

The MERV is calculated using a series of tests to determine efficiency of the air filter.

The test involves injection of particles in twelve different sizes into an air stream that passes through the air filter. By counting the airborne particles of each particle size, the efficiency of air filter is determined. The test is repeated six times for each particle size and the lowest values are then used to calculate the Composite Minimum Efficiency Curve for that air filter. The twelve size ranges are then distributed into three larger groups, namely E-1, E-2 and E-3. An average of the Composite Minimum Efficiency for each group is used to find out the average Particle Size Efficiency (PSE) of the air filter. Finally, the percentages are used to calculate the MERV rating of an air filter.The MERV is an industry standard that allows comparison of filters made by different manufacturers.

The MERV is a standard rating system that helps to compare the efficiency of an air filter made by different manufacturers.

The MERV has a numerical value ranging from one to twenty. The higher the MERV rating, the greater the filter's efficiency in capturing and holding out dust particles of smaller specified size ranges. Air filter with an MERV 1 through 4 will be most effective in removing large, dust particles. These flat or panel air filters are commonly used in residential furnaces and air-conditioners. Such air filters are generally used to protect equipment and in light industrial and residential projects. As they have low efficiency, they are not used directly to maintain indoor air quality. Air filters with MERV rating of 5 through 13 are great at removing finer dust particles. These pleaded or extended surface air filters have medium efficiency and are fairly efficient at removing small to large airborne particles. Although they are almost as effective as HEPA filters, they are much less expensive and can filter out most airborne indoor particles. Due to less airflow resistance, these air filters have a quieter HVAC fan operation and higher airflow rates than HEPA filters.

Air filters with higher efficiency are often mistaken for HEPA filters. Air filters with higher MERV rating of 14 to 16 are often misidentified as HEPA filters. They are widely applied to remove contaminants and particles that may harm human health and productivity. They are commonly installed in hospital inpatient and general surgery areas, and some of the best commercial buildings. An Air filter with MERV rating of 17 through 20 is used in clean rooms and pharmaceutical manufacturing premises. In these areas, maintaining the highest standards of cleanliness and removing airborne dust particles is of utmost importance so that product quality may not get affected.