Noise Insulation for a Furnace Duct

Duct Sealing

• One important aspect to eliminating both heat loss and excess noise in your furnace duct work is to properly seal the duct work. Despite conventional wisdom, duct tape is not a good tool for this task. Duct tape does not create a truly air tight seal and deteriorates quickly. Instead, seal the openings in your duct work with mastic sealant or metal tape.

Insulation

• Once the furnace ducts have been well sealed, insulation is the next step to reducing both heat loss and excess noise. The US Department of Energy recommends rigid foam board insulation for this task, but for maximum noise reduction, consider the use of acoustic panels or soundproofing duct wrap, available from a variety of manufacturers. Simply wrap the insulation around the ducts and secure them exactly according to the manufacturer's instructions.

Installation Tips

• In terms of heat loss, it is most important to insulate ducts that run through unfinished parts of the home, since these areas will have more of a temperature differential between the duct and the air outside of the duct. But it is also important -- particularly for reducing noise -- to insulate ducts in finished parts of the home as well. Note, however, that ducts in these areas generally require less insulation than those in finished areas of the home.

R-Values

• Insulate your ducts to their recommended R-values for maximum noise reduction and increased efficiency. R-value depends both on the part of the home in which you are insulating the ducts and on the climate in your geographic area. Warm climates with hot summers and mild winters need R-4 to R-8 insulation on ducts; mixed climates with slightly colder winters require R-2 to R-8 insulation around ducts and the coldest climates in the US benefit from R-2 to R-11 insulation. Calculate the R-value of a single layer of the foam board insulation you purchased and wrap the ducts with enough layers to achieve the desired R-value.