RACO’s plenum-rated boxes are used in above-ceiling applications where airtight enclosures are required, for use in air returns or where code requires. Knockouts on these new plenum boxes are airtight. The 4-in.-square models provide a variety of ½- and ¾-in. knockout options. They are available in 4- square, 4-11/16-square and 4-in. octagon box styles.