In big commercial and institutional buildings, the mechanical noise of HVACs can be a big deal—and big dollars are spent on to be quieter. In the world of home building, the problems aren’t so extreme. But the principles are the same: to keep noise out of the living space, you try to disconnect the source of the sound waves from the pathways that could carry them into the living space. And use materials that absorb sound rather than reflecting or passing it.
A common complaint in single-family and multifamily homes is that ducts carry the sound of music, laundry, dishwashers, or even just conversation across or around the walls that are supposed to create privacy, peace, and quiet. Metal ducts transmit vibration easily, and they reflect sound waves along the length of the duct. Even a short area of insulated crooked duct at the end of a duct run can help hush that kind of sound transmission.
HVAC machinery sometimes sends an unwanted sounds like hum, purr, buzz, or roar into the living space—again, transmitted easily along metal ducts. Disconnecting the metal duct from the machine with a soft, flexible covering can help. Another solution: instead of metal ductwork, use fiberglass duct board that’s designed to absorb sound instead of transmitting it.