Many home theaters are plagued by noise from forced air heating and cooling systems. Reducing this noise can make a huge impact on the theaters sound quality. Because it may not be possible to move or redesign the room and all homes are different it is necessary to consider several solutions. There are three sources of noise to look for from these systems. They include noise from the airflow, fan and duct vibration.
The level of noise caused by air flowing from the registers is proportional to the velocity of the air flowing and how far they are from where you sit. Velocities can be kept low with variable speed motors, more registers and a bypass damper on zoned systems. The bypass damper can also reduce noise from air leaking through a zone damper.
Air leaks at the air handler can also generate considerable noise. If you hear whistling in this area leaks are the likely cause. These can be reduced by carefully sealing all of the duct work around this unit with aluminum tape. Note that corners frequently have large leaks.
Fan noise can be a big problem because many home theaters are located near the air handling unit in the basement. Seal all of the doors into the room that contains the equipment like it was an outside door with weather stripping. Adding an additional layer of sound proofing like a sound blanket over the door in the air handling room can also reduce the sound that penetrates the door. Using a door with a high sound isolation rating can help. Insulating the walls can help. Insulating the air handling unit and ducts will also reduce the noise from this system.
Duct vibration can also be created by the fan. This can be reduced by insulating the ducts with a heavy foam product that damps the vibrations.
It should be noted that many of these steps will also improve the efficiency of your heating and cooling.
Be careful that any changes you make do not cause a fire or electrical hazard with these systems!