A fan filter unit (FFU) is a type of motorized air filtering equipment. It is used to supply purified air to clean rooms, laboratories, medical facilities or micro-environments by removing harmful airborne particles from recirculating air.The units are installed within the system's ceiling or floor grid. Large clean rooms require a proportionally large number of FFU, which in some cases may range from several hundred to several thousand.Units often contain their own pre-filter, HEPA filter and internally controllable fan air distribution.