Ordinary vacuum cleaners pick up dirt from a carpet, filter out the larger, harmless particles, and throw a majority of the harmful allergenic, irritating, and toxigenic particles back into the air. If you do not breathe them before they settle out of the air, you then have the chance to try again next time.

Filters in central ventilation systems should be the most efficient that the system can handle. Even then, they will not function effectively if the fan is not running on the system. Since many people use their systems only a portion of the time, that makes room air cleaners often a better choice for filtration.  If you have chosen a room air cleaner of good efficiency, it may still do no good at all. It has to process enough volume of air. There is a rating system, "CADR," or clean air delivery rate, which can be used to judge whether the air cleaner is large enough for your intended use. Manufacturers typically state these in terms of the number of times per hour the device will clean the air in a given size room. No filter or air cleaner will do much good if there are doors or windows open (bringing in new air faster than you can clean it) or if the interior of the building is filthy or has a major source of contaminants, such as an active mold growth problem.  Also, room air cleaners should blow out the top, not out the bottom, where they will blow dust out of the carpet or surface they sit on. Such a setup can actually increase the amount of allergens in the air.

The following are the main types of filters. These are found in central heating and air conditioning systems, and also in room air cleaners, and some types of vacuum cleaners.

There are basically three ways to keep the air inside of a building clean: Do not let contaminants in; filter them out of the air; and remove them from surfaces by cleaning.

Contaminates that affect air quality are either in the form of gases, or in the form of particles. Particles accumulate in dust on surfaces. Dust inside a building typically contains bacteria, various kinds of mold spores, fiberglass, and other irritating, toxic, and allergenic materials. The more dust, the more of these materials are present. Occupant activities stir up the dust, which is then inhaled by the occupants, or lands on their skin, or falls back out of the air, until the next time it is disturbed. Numerous studies have demonstrated that the cleaner the air, the healthier the air. In fact, for every increase in the amount of dust in the air, there is a measurable increase in allergy and asthma attacks, emergency room visits, and deaths. This effect is measurable even at very low levels.