Function----Louvers permit free air passage, controlling the volume by their size or design. They diffuse or control direction of air flowby blade design.
Insert louvers---- Louvers commonly used in standard steel doors are of the "insert " type designed to be mounted into a cutout in the door and an overlapping frame. Inverted "V" blade, "Z" blade, inverted "Y" or chevron-type blade, light proof, adjustable blade, grille type, and fusible link self-closing fire door type are available in a wide range of sizes. Also available from some steel door manufacturers is a pieced louver design. Insert louvers intended for exterior doors or other doors where security is a consideration should have fasteners or materials specified accordingly.