Air filters and air cleaners essentially take in air, filter out particles and blow the cleaned air back through the central heating and cooling system.  How efficient a filter collects the particles is rated as MERV (Minimum Efficiency Reporting Value).  The higher the MERV rating, the smaller the particles it can filter out.

Dust-Stop Filter. (MERV 1-4)   Also known as the supermarket special, “3 for a dollar” throw-aways, are available in thicknesses from 1/2", 1" and 2".  Their task is to protect the blower compartment from large particles of dust and lint.  They need to be changed once a month to offer reasonable protection for equipment.

Electrostatic Filter. (MERV 1-4)   Charging filters operate on the principal of static electricity.  Air rushing through the filter creates an electrostatic charge. You experience the same effect if you rub a balloon on your arm and stick it to a wall.  The drier the air the better they work.  However, their efficiency drops rapidly as relative humidity increases.

Media Pleated Filters and Media Panel Filter. (MERV 6)  Media pleated filters use a cotton/polyester blended media arranged with pleats within a frame.  Media panel filters use a fiberglass and synthetic media in a flat panel frame.  By increasing the collection surface area it’s possible to obtain a MERV 6.

Pleated Filter. (Electrostatically Charged).  (MERV 9-12)  Also known as high efficiency pleated filters. They use 100% synthetic media (similar to the electrostatic filter) arranged with pleats within a frame.  By adding an electrostatically charged media it’s possible to obtain a MERV 8.

Rigid Box Pleated Media Filter. (MERV 9-12)  Ridge Box is a galvanized box that is attached to the return air side of a central air system.  The media pleated filter used is either a cotton/polyester blended media or 100% synthetic fibers.  Because of the large (4" thick) pleated filter it’s possible to obtain a MERV 9-12.

Electronic Air Cleaner. (EAC) (MERV 8-10 )  Just like the rigid box for the Pleated Media Filter Ridge Box, the EAC is a galvanized box containing the EAC, and is attached to the return air side of a central air system.  When this air goes through an electronic air cleaner, the pre-filter traps the majority of the large particles.  Smaller particles flow through this pre-filter to the cell where they’re hit by an electric charge.  Collector plates, which carry a negative charge, attract these small particles like magnets, holding them until they’re washed off.

HEPA Filter. (High Efficiency Particulate Air). (MERV 17-20)  HEPA filters are installed as a stand alone ridge box that’s attached to the return air side of a central air system.  The filter housing system also contains its own motor that pulls air within the duct system, filters out the particles and then blows the cleaned air back into the duct system.  HEPA filters are very thick and tightly pleated filters that remove even very small particles very efficiently.  With a HEPA system it’s possible to obtain a MERV 17-20.

Warning! Before you invest in any high efficiency filter it's important that you read... The Downside Of A High Efficiency Filter.

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