Traditionally forced air heating and air conditioning units had no governing standards for establishment of quality of filtration systems.
Moreover, performance was judged by individual businesses and homeowners by the amount of deposited particulate of dust, lint, dirt and dander that would build up on the surfaces of ductwork, fan blades and heat and cooling exchange units downwind of any filter placement, assuming any was in use.
The large majority of HVAC (heating ventilation and air conditioning) units still in use today in private residences and small businesses operate more than adequately and more energy efficient, with less fatigue on the equipment by using minimum efficiency panel filtration products.
However, in recent years concern over indoor air pollution and the possibilities of spreading infectious airborne pathogens on minute particulate of less than 10 microns has forced the HVAC industry to require higher efficiency filtration products for commercial / industrial as well as modern residential high energy efficiency HVAC units that reduce initial resistance to air movement, yet conserve energy required to do so. The American Society of Heating, Air-conditioning and Refrigeration Engineers (ASHREA) developed a Minimum Efficiency Reporting Value (MERV) scale to establish a measure of performance in a filtration system or product.
Merv 5 to 8 rated filters are a better choice and are more commonly found in commercial applications. These filters will collect particles as small as 3 microns and are a good choice for home owners with modern heating systems designed to work efficiently with them.
Filters with a merv rating of 9 to 12 are used in commercial and industrial applications and will stop particles in the 1 to 3 micron range. These filters are a great choice for home owners who want the best dust control possible. When using filters with Merv 9 ratings and above it is important to clean or replace them when recommended by the manufacturer because they will have a negative effect on air flow when they become dirty. This can lead to performance problems and decreased operating efficiency.
The most efficient filters have merv ratings of 13 to 16 and will stop particles as small as .3 microns. These filters are used in hospitals and other super clean environments.
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