HEPA Air Filters - How do they Compare?

There are several other types of air filters and air cleaners besides HEPA air filters. The HEPA air filter is a type of mechanical air filter which works by capturing particles on the filter medium. One of the reasons that HEPA filters are so efficient is their thickness - usually 11 1/2 inches thick compared to 1 inch to 4 inches of disposable filter refills of other types of mechanical air filters.

Other types of air cleaners include electronic air cleaners and electrostatic air filters. Electronic air cleaners have a series of electrically charged wires arranged in a grid. Air particles are forced past the wires by a fan, and the electrical charge of the wires attracts dust particles.

Unlike mechanical filters, electronic air cleaners become less efficient the more they are loaded with particles. In order to maintain their top efficiency, they must be cleaned frequently. Even at their highest efficiency, though, they are much less effective in trapping air particles than HEPA filters.

Electrostatic air filters are made from polyester or polypropylene strands. They are usually attached to an air filter frame on a furnace or air conditioner. These filters are very popular, but are very inefficient, usually carrying about a 4 MIRV rating. One of their advantages is that they can be rinsed off with water and reused.

Negative Ion Generators

These devices emit negative ions which change the electrical charge of air particles. These negatively charged particles are then attracted to surface areas with a positive electrical charge such as the wall, the floor, furniture or the ceiling. If these particles lose their negative charge, they are released back into the air, so negative ion generators are not an efficient air cleaner and should only be used in conjunction with another type of air filter.