The Vornado AC550 uses true HEPA filtration, one of the most effective filters available, to remove up to 99.97 percent of airborne allergens down to .3 microns in size. AC550 actively circulates and filters all the air throughout a room. Without powerful circulation, an air cleaner only cleans the immediate area around the unit. The AC550 uses a radial blower to intake and clean all the air in a room. Up to 335 sq ft. Precision engineering allows the blower to operate quietly, despite it's powerful airflow. The AC550 uses a combination of 2 HEPA and 2 carbon filters to trap dust, pollen, pet danger, smoke, bacteria, mold spores, dust mites and more. The carbon prefilter both absorbs odors and traps larger particles. When in auto mode, advanced dust sensing technology detects the level of dust in a room, fluctuating the cleaning cycle up or down, depending on the air quality. Featues 4 speeds, push button electronic controls, filter replacement indicator and sleep mode.