Q:  What product should I use to reduce the sound level from noise generated within a return air plenum?

A:  A fiber glass batt with a minimum thickness of 3 ½ inches. The batt will reduce the amount of sound that is transmitted through the ceiling. Additionally, Johns Manville fiber glass batts have been tested for air erosion resistance according to Underwriters Laboratory (UL) test method 181. Fiber glass batts can be used in return air plenums with air velocities of 1000 feet per minute or less.