AB: Air is filtered when it's brought back through a unit to be conditioned and then redistributed. In a car, the air filter prevents dirt, debris, and impurities from getting into your engine and dust, pollen, dirt, and other pollutants from getting into your air and heat vents.
SS: The air filter allows the air from your heater and air-conditioner to pass through to the duct system in your home, while at the same time trapping the small particles in the air in hopes of not letting them pass through to the rest of the house. This allows the air passing through your ventilation system to have less of a chance of spreading around irritants that can be inhaled.
JM: The types of air filters people most commonly use in their homes are known as mechanical air filters. These are filters for use in an HVAC system. Disposable filters need to be replaced and systems cleaned at regular intervals. Mechanical air filters work by trapping particles from the air onto the filter. High efficiency particulate air (HEPA) filters are a type of high efficiency mechanical filter. While mechanical home filters can trap everything from dust to cockroach allergens and pet dander, they don't trap gases