Basically, fiberglass filters screen out some dust and larger particles, but let many smaller particles pass through. These filters can last up to 90 days, but a filter should be changed sooner if it becomes very dirty. Pleated filters generally have significantly better efficiency at removing dust and smaller particles than fiberglass filters. These are the best filters, and manufacturers often claim efficiency ratings of 90 percent or higher and the ability to screen out extremely small particles. Electrostatic filters are generally cleaned by rinsing them with a stream of water.
WEB also makes a special spray cleaner.
Electrostatic filters have no wires and do not require electrical current to operate. The filters have a built-in charge of static electricity that is activated by the friction of air passing through the filter material. The static-electricity charge attracts and holds tiny particles that would otherwise pass through. The Filtrete typically lasts about three months. If in doubt about how to set the control, have a technician do it the next time the equipment is checked.