Air cleaners are generally classified according to the technology employed to remove various sized particles and/or gases from the air. The general types of technologies available for use in these include mechanical filters, electronic air filters and hybrid filters for the capture of particles and gas phase filters to control odors. Those which operate by chemical process, such as ozonination, also exist. The selection of a type of air cleaner should depend on the intended use of the filter. 

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Filters' wide applications include:

1. protecting the HVAC equipment and components,
2. protecting the furnishings and decor of occupied spaces
3. reducing housekeeping and building maintenance
4. reducing furnace and heating equipment fire hazards
5. protecting the general well-being of residents.

The first four of these applications can be accomplished with the lower efficiency filters generally used in central HVAC systems. The last, which has to do with health issues, will require much higher performance filtration.

It may not always be possible to install this equipment in older existing environmental systems. Thus, self-contained portable room filters must sometimes be used to obtain sufficiently high levels of filtration effectiveness.

The reality in most residences is that total elimination of a pollutant source is not always possible or practical. Individuals with severe allergy and asthma symptoms, whose symptoms are not alleviated by other source control and ventilation strategies, may want to try an effective filter in an attempt to aid in further exposure reduction. Although there is no proven health benefit from such a measure, some individuals report that they perceive filter as useful in improving their health status.