HVAC (Heating, ventilation and air-conditioning duct) are usually wrapped in fiber glass for thermal insulation. Fiber glass also have good sound absorbing properties and help in the breakout noise from the sheet metal duct. Jute-based composites have yet another application for noise control in ducts. The jute felt faced with a jute textile is applied to the inner walls of the duct. Since jute felt have good sound absorbing properties they help in the noise reduction. Since they are faced with jute textiles, the fibers do not separated due to the flow of air in the HVAC duct. It is recommended by ASHRAE (American Society of Heating, Refrigeration and Air-conditioning En­gineers) that the maximum flow velocity of air at the exit of a duct from an AHU (Air Handling Unit) should be less than 7.5 m/s64. At these speeds in the duct the fibers do not separate from the felt. Figure 6.24 shows a sheet metal duct lined with 25 mm jute felt faced with jute textile of 400 gsm (grams per square meter). Fiber glass is not rec­ommended to be used inside a duct, since if the fibers get carried by the air flowing inside the duct, they can be harmful to persons breathing the conditioned air, which is not so in the case of jute. Jute being hygroscopic can also withstand and moisture or condensate getting deposited in it in the inner of the duct walls. Jute felt can also be wrapped outside the duct to reduce the breakout noise.

The inside linings of AHU (Air Handling Units) of HVAC systems can also be lined with jute felt with a perforated facing backed with a 5 mm thick composite jute panel, for substantial noise reduction. Particularly in hospitals and classrooms where low noise levels are required, such a treatment can be done.