Panel filters are the most common type of filter used in residential HVAC systems. They get their name because they are flat, and rectangular or square, which makes them resemble a panel. They generally protect the motors, fans and coils of HVAC systems from getting a buildup of dust, dirt and debris. This type of panel should be replaced yearly, or more often if the home is in a dusty or sandy area. These filters are primarily protective of the HVAC system and are not designed to improve air quality.
Electrostatic filters use static electricity to remove particles from the air. When the air passes through the front of the filter, the first two layers of the filter charge any particles with static electricity. Then, as the particles move through the rear two layers, which have the opposite polarity of the particles, the particles attract and stick to the rear layers. There are electrostatic filters that will fit most HVAC systems, and they can replace most panel filters.
Electrostatic filters give better filtration than standard panel filters with fiberglass. The electrostatic charge is built into the filter, so there is no need for electricity.
Pleated filters are an upgrade in efficiency compared to standard panel filters and are about as efficient as electrostatic filters. Pleated filters gain efficiency because they have an increase in surface area, allowing better air filtration. The material of the filter is folded back and forth, thus increasing the filter's surface area.
Washable filters are generally made of foam. As the name implies, they can be washed and reused. This type of filter came into use because manufacturers wanted to save the consumer the cost of purchasing new filters. This type of filter is not in wide use except in small HVAC systems, such as window-size air conditioners.
HEPA filters were first brought into use in hospitals, for food industry uses and for other corporate uses where air needed to be very clean. They are now becoming more popular in a wide variety of residential uses because of their extreme efficiency. A HEPA filter is capable of removing 99.97 percent of all dust, mold, allergens and other particles from the air. HEPA filters are being installed not only in HVAC systems but also in anything that has air flowing through it, such as vacuum cleaners.