Noise from air ducts---the tubes made of sheet metal that carry warm and cool air to vents---can be a big distraction. If you are trying to sleep, work, watch TV or even carry on a conversation and the noise is interfering, it's time to implement a buffering strategy.
Planning Your HVAC System
If you are building a new house, make sure the air duct system is designed so that the noise will not interfere with daily activities. The fans and blowers within the duct system are usually the source of the noise, though sometimes the sheet metal construction of the ducts themselves can clang together.
Hire a reputable HVAC subcontractor to design and install the system, and consider having a mechanical engineer review the final design. Noise generating components of the system should be located over spaces in which you don't spend much time: closets, laundry rooms or bathrooms. It is especially important to design the system so that living and sleeping spaces stay quiet. The air ducts also need to be sized properly to prevent additional noise.
Insulating Air Ducts
Since air ducts will make noise no matter how well the HVAC system is designed, properly insulating them is the best strategy to reduce this noise. It also increases the energy efficiency of your heating or cooling system.
In an existing home, you can usually access air ducts through attic or crawl spaces or the basement. Fibreglass insulation is typically used around ducts. Be sure to choose the right R-value, the insulation's resistance to heat flow, depending on the type of heating system and the climate in which your home is located.
Air Duct Silencers
Since ducts act as 'sound tubes' that amplify the sound of the fans and blowers around the house, consider installing air duct silencers. A variety of these products are on the market. They can easily be installed in existing systems. Sound absorbing materials are placed on the inside of the duct and can eliminate some of the sound that external insulation cannot.
Expansion Joint Collars
Some air duct noise is caused when the connections of larger and smaller sections clang or rattle due to expansion and contraction of the metal. By installing adequate expansion joint collars, much of this noise can be eliminated. Hire a heating and cooling professional to examine your system to make sure ducts have plenty of clearance and aren't banging against PVC plumbing pipes, structural members or other framing elements.