- Jan 28, 2019-

Listed fusible-link type louvers to a maximum size of 24" x 24" are permitted in 1-1/2-hour and 3/4-hour fire doors, with the louver mounted in the bottom half of the door. Louvers may not be used in 1/3-hour (20 minute) rated doors, or doors of other hourly ratings that may be part of a smoke and draft assembly. Doors with glass lights, or doors equipped with fire exit devices may not have louvers.