Ideal-Air� HEPA Intake Filter Boxes are the first in their class of inline filtration, with the HEPA filter fighting against incoming contaminants. Each galvanized metal box has an easy open lid that connects easily to duct work. HEPA filters have many applications, including use in medical facilities, automobiles, aircraft and homes. HEPA blocks pollen, dust, bugs and other particulates from entering. Available in sizes 4 in - 14 in. Filter included. Replacement filters sold separately.