Fiberglass is back, in a big way, as an interior duct liner. Actually, it was never gone, but IAQ concerns made it a back-burner option.

Fiberglass is back, in a big way, as an interior duct liner. Actually, it was never gone, but indoor air quality concerns made it a back-burner option for some contractors and specifiers.

Today, earlier concerns have been largely overcome and the product actually is now being touted as an IAQ enhancer rather than a contributor to IAQ problems.

Good news for fiberglass came when the International Agency for Research on Cancer (IARC) lowered the classification of international glass wool, rock wool, and slag wool fibers from a Group 2B classification (?possibly carcinogenic to humans?) to a Group 3 classification (?not classifiable as to carcinogenicity to humans?).

IARC emphasized that ?Epidemiologic studies published during the 15 years since the previous IARC Monographs review of these fibres in 1988 provide no evidence of increased risks of lung cancer or of mesothelioma (cancer of the lining of the body cavities) from occupational exposures during manufacture of these materials, and inadequate evidence overall of any cancer risk.?

The reclassification was hailed by the North American Insulation Manufacturers Association (NAIMA). President Ken Mentzer said ?the IARC re-evaluation confirms NAIMA?s confidence in the safety of its members? products for workers and consumers when proper work practices and installation methods are followed.?

According to the IARC, this study distinguishes fiberglass from asbestos, ?a known human carcinogen which causes both mesothelioma and lung cancer and? is extremely slow to decompose and disappear from body tissues in which it has been deposited? which is known as high biopersistence.

?In contrast, the more commonly used vitreous fibre wools including insulation glass wool, rock (stone) wool and slag wool are now considered not classifiable as to carcinogenicity to humans (Group 3). Continuous glass filaments, which are used principally to reinforce plastics, are also considered not classifiable as to carcinogenicity to humans.?

Keeping contaminants out

“Fiberglass insulation can be used to prevent the introduction of any unwanted ‘stuff,’” points out Eric Schakel, business manager for Johns Manville. That “stuff” includes the more obvious airborne contaminants such as dirt and fibers, but also extends to water and noise. Insulation can be used effectively to prevent condensation, as well as to reduce in-duct rumble from the air handlers and fans. The use of insulated duct also saves energy.

“Many of the new coil lines being sold are coming with insulation installers built in,” Schakel said, “or the older ones are being retrofitted easily enough.”

There have been acceptably formulated alternatives to fiberglass, such as Johns Manville’s Polycoustic. These products provide a reasonable alternative with some of the same beneficial properties as fiberglass, but are more expensive. Fiberglass is still the most economical way to line a duct.

Johns Manville also has a relatively new duct sealant used to seal any fiberglass that is exposed when lined duct is cut into for job-site assembly. Other companies make such products as well; Johns Manville calls its product Super Seal, and another version is known as Duct Butter. These prevent any stray cut fibers from finding their way into the duct’s airstream, and are simple for a contractor to use. They come in a spray can or can be brushed on. Duct Butter, in addition, has an R-value of 3.6, so it acts as an insulator along joints and edges in applications where energy saving is important.