Flow Sciences FS4500 Dual Stacked HEPA Vented Balance Enclosure Accessory. The FS4500 dual stage filter housing is used when both particulates and odor abatement is required and house exhaust is not available in the facility. The FS4500 uses both a HEPA and Carbon filter to completely filter air and safely recirculate back into the room. Internal fan, 110-120v, 60 Hz. With pressure gauge used to determine when filter change is necessary.