AHU (Air Handling Unit) HVAC FILTERS A particulate air filter is a device composed of fibrous or porous materials which removes solid particulates such as dust, pollen, Mold and bacteria from the air. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines. An air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating, ventilating and air-conditioning system. The basic function of the AHU is take in outside air, re-condition it and supplies it as fresh air to a building.