Mechanical air filters are one of the 3 major methods to clean the air in your home.

Air filter can be effective if regularly maintained

Mechanical filters may be installed in ducts in homes with central heating and/or air-conditioning or may be used in portable devices which contain a fan to force air through the filter. Mechanical filters used for air cleaning are of two major types.
Flat or panel filters generally consist either of a low packing density of coarse glass fibers, animal hair, vegetable fibers, or synthetic fibers often coated with a viscous substance (e.g., oil) to act as an adhesive for particulate material, or slit and expanded aluminum.

Flat filters may efficiently collect large particles, but remove only a small percentage of respirable size particles.
Flat filters may also be made of "electret" media, consisting of a permanently-charged plastic film or fiber. Particles in the air are attracted to the charged material.
Pleated or extended surface filters generally attain greater efficiency for capture of respirable size particles than flat filters. Their greater surface area allows the use of smaller fibers and an increase in packing density of the filter without a large drop in air flow rate.

Because higher efficiency pleated filters are much thicker than filters generally used in standard home heating and/or air-conditioning systems, their use results in substantial air resistance, so they cannot be directly incorporated into the standard residential system. Instead, a system must be specially designed with a fan of sufficient power to create the necessary air pressure and with one or more efficient pre-filters Costs for installation of the system, replacement of pre-filters and filters, and system operation should be considered before deciding whether to purchase higher efficiency filters

The basis types of air filters

Cost and maintenance requirements should be a key consideration when you explore what type of air filters you are going to select. The basic types of air filters include:

Panel filters

Panel filters are inexpensive to buy-they cost between 50 and $5-but they have dust-spot efficiencies of less than 5%. Their filtering capability actually increases as they get dirty, but this is accomplished at the expense of restricting air flow and increasing pressure drop. To avoid restricting air flow, they should be changed every one to three months. They do a poor job of protecting the forced-air system and offer human lungs almost no protection from particles.

Electrostatic air filters

Electrostatic panel filters are a little more effective than standard panel filters because they rely on static electricity to attract charged particles in the airstream. Either the static electricity is created by air as it flows through the filter, or the filter is manufactured with precharged electrets made from a propylene, polypropylene, or other plastic material. The electrets are permanently charged with both positive and negative charges. As air flows past the charged filter material, oppositely charged particles in the airstream cling to the filter's fibers.

High-Efficiency Particulate Air Filters (HEPA)

High-efficiency particulate air (HEPA) filters achieve the maximum efficiency available, with dust-spot and DOP test values greater than 97.99%. However, HEPA filters greatly restrict air flow and require special blowers and duct design. They are usually found in "clean room" applications in industrial or commercial settings, rather than residences

Extended surface filters

An electronic air cleaner, or electrostatic precipitator, uses high voltage to charge particles in the return airstream. The charged particles are collected on an oppositely charged metal plate. Electronic air cleaners achieve dust-spot efficiencies of over 90% with little air flow restriction

Editors' Top Picks

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Quality filters for air conditioning and furnace filters that capture dust and other airborne pollutants with the power of static electricity. Filters have anti-microbial media to inhibit the growth of mold and bacteria. See how you can protect your home or office by visiting www.air-care-filters.com Editors Pick!

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A great resource from the college of NC State university college of agricultural and life sciences on air filter technology and what to look for in air cleaners.

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