Different Types For Different Jobs

Duct liner is typically applied to sheet metal ducts while they’re being constructed in the shop. Contractors often use a coil line, which will automatically adhere the liner to the sheet metal itself. Once the duct liner is adhered with glue, the coil line inserts metal pins through a spot-welding process.

There are different thicknesses of duct liner, usually 1/2, 1, 1 1/2, and 2 in., as well as different types of liner itself. In the industry there is short fiber duct liner and long fiber duct liner. Each can be beneficial depending on the application.

The long fiber duct liner is typically made from a textile-based fiber; these fibers are longer and larger in diameter. The benefits are that the product is tough, durable, and stands up to abuse well during fabrication and installation, and during transportation and handling. The industry refers to this liner as “textile duct liner.”

“Typically, a sheet metal shop will cut the sheet metal to size and adhere the duct liner, bend the sheet metal into L sections, stack those Ls up together and throw them on the back of a truck to transport to the jobsite. Fabrica-tion will then take place on the job site by putting the two Ls together to make a duct section,” says Dave Tomchak, hvac/industrial marketing manager, CertainTeed, Valley Forge, PA.

Textile duct liner (offered by CertainTeed as “ToughGard”) is very good in these instances, because it’s durable and stands up to the loading, unloading, and other abuse. While the ToughGard product is very durable, its acoustical properties are not quite as good as those found in a short fiber duct liner. Due to their larger fiber diameter, a textile duct liner will have a slightly lower R value and noise-reduction coefficient (NRC) value. In actual practice, however, these values do not result in any significant performance differences.

“The R value and the NRC values are typically slightly lower with a textile-based product than with a short fiber-based product,” notes Tomchak.

However, a short fiber-based product is inherently not as durable and does not stand up to abuse as well. Yet the advantages of using a short fiber product are that the R values and NRC values will be higher. A short fiber product such as ToughGard R will probably work better if an owner is more concerned with R values and acoustical properties. It is best to check the building code or project specification to determine which product is most appropriate to use.

Resists Moisture

Because indoor air quality is a big issue in commercial buildings, CertainTeed now offers both ToughGard and ToughGard R with an enhanced surface. The enhanced surface was developed to help alleviate concerns about moisture that may enter a duct system due to improperly sealed duct joints or poorly installed and maintained hvac systems.

The enhanced airstream surface contains an EPA-registered antimicrobial agent in order to reduce the potential of microbial growth that may affect this product.

Tomchak notes that if a system is improperly maintained or installed, moisture and dirt may become present in the ductwork, resulting in mold growth. “From a manufacturing standpoint, we’re doing our best to reduce the possibility of that happening,” he says. “If moisture is present inside the duct, perhaps due to condensation or cooling coil blow-off, our duct liner surface will repel it. Repelling it will help keep the moisture on the airstream surface so that it can be evaporated by the airflow rather than being absorbed into the duct liner.”

Both ToughGard and Tough-Gard R provide high resistance to tearing and puncturing during fabrication, installation, and cleaning (using industry-recognized duct-cleaning equipment outlined in the NAIMA “Duct Cleaning Guide”). Both liners also improve system thermal efficiency, exhibit low air resistance, and reduce the potential for fiber erosion.

If the system is maintained properly, the duct liner will not degrade. As Wayne Shaw, hvac/industrial technology manager for CertainTeed notes, “The product itself, from a longevity standpoint, should last the lifetime of the duct — there’s no reason to believe it’ll deteriorate if it’s well maintained.”

Who knows — maybe duct liner will help alleviate that age-old problem of office gossip. Or at least it will make eavesdropping a little more difficult.

Publication date: 10/22/2001