This type of filter comes with a lifetime guarantee, but should be cleaned once a month. Another type of filter which requires duct work is a mechanical four-inch pleated filter. It consists of a sponge like material which catches dirt and should be changed every nine to twelve months. The most effective filter is an electronic filter which has electrical power going directly to the filter. The dust particles cannot go back into your heating or cooling system because they become electrically charged.
Electronic filters are the most effective filters for highly sensitive people.
When purchasing an air cleaning system you should first consider cost, productivity, ease of installation, and upkeep. The one-inch throw away filter is the cheapest, but it only filters out large debris. They are easy to install, but must be changed often. Electrostatic filters are sensibly priced, and usually comes with a lifetime guarantee. They will remove very tiny particles, are installed in the same way as the one-inch throw away filters are, and must be flushed with water once a month.