Mechanical-electronic hybrid filters are a combination of the two filters mentioned above. For example, an "electret" filter uses an electrically charged flat or pleated fabric to attract airborne particles.

• Gas phase filters may be attached to air cleaning devices to filter specific gases, vapors, and odors since neither mechanical nor electronic filters can remove gases and odors on their own. These air cleaning units may be equipped with a chemical filter designed to removed pollutant gases from the air; activated charcoal is most widely used. Other substances used in these filters may include silica gel, activated aluminum coated with potassium permanganate (which is fairly effective in capturing formaldehyde from the air), zeolites, porous clay minerals, or molecular sieves. These filter materials may become quickly overloaded and need to be replaced often. As a result, these devices are more expensive to buy and maintain. Gaseous pollutant air cleaners are generally rated in terms of the total amount of a chemical that can be captured.

There are three types of air cleaners: mechanical filters, electronic cleaners, and hybrids that are a combination of these two.

Mechanical filtration: These draw air through a flat, pleated, or high efficiency particulate air filter to trap particles.
Some of the purposes of air filters are:

• Protect the ventilation equipment from dust and dirt
• Protect furnishings and décor of the occupied space
• Reduce housekeeping and building maintenance
• Reduce furnace and heating equipment fire hazards