The vast majority of installations specifying flexible closed-cell elastomeric duct liner have been for traditional rectangular duct.

But liner is being used on spiral duct HVAC construction projects. K-Flex USA Duct Liner Gray has been used successfully on several spiral projects. The Ecole K.B. Woodward Elementary School in Surrey, British Columbia, is one such example. 

Spiral ductwork has some obvious benefits with respect to indoor air quality. The lack of corners minimizes dead spots where dirt and spores can potentially collect, providing a potential food source for mold and bacterial growth. The selection of a flexible closed-cell elastomeric duct liner for use with spiral duct provides the ultimate system for indoor air quality, environmental comfort and cost effectiveness.

Flexible closed cell elastomeric liners are specified for several reasons. Their closed-cell structure makes them naturally resistant to moisture. They have very low permeability and water absorption, and they perform without the need for facing, which can become damaged or delaminate over time. They can be cleaned when necessary, and are not affected by commonly used cleaners. They do not contain mineral fibers, and several products on the market, including K-Flex Duct Liner Gray carry an Underwriters Laboratories’ Greenguard and Greenguard Gold certification for volatile organic compound emissions. 

lined round ductwork in classroom

K-Flex Duct Liner Gray is formulated with an integral anti-microbial agent. Additionally, closed-cell elastomeric insulation provides the necessary insulation to comply with energy codes as well as to prevent condensation. One of the unique features of closed-cell elastomeric insulation is that it provides both adequate levels of sound absorption, limiting noise at the diffusers in addition to controlling breakout noise, reducing the amount of noise radiated through the duct and into the environment. This is especially important in a classroom, where unwanted noise can become a distraction or a hindrance.


Pat Barlee of installing sheet metal works contractor Crosstown Metal Industries Ltd. said proper installation of closed-cell elastomeric liner can be challenging, especially in single-wall construction. But it is getting easier. Fast tack water-based adhesives provide a solvent-free adhesive option for installation and also allow some time for making adjustments to the liner positioning. And capacitor discharge welders now available from several manufacturers offers a mechanical fastening method that minimizes smoke generation and damage to the liner and ductwork. In the handheld version, it has the added benefit of being smaller and lighter than traditional resistance welders, making it easier to maneuver in tight spaces such as small diameter spiral duct.

Limitations remain when combining spiral duct and closed-cell elastomeric insulation. For single-wall or double-wall construction, maximum duct lengths are dictated by duct liner roll width and arm length. Typical working length would be 4 to 6 feet for single wall, but longer lengths (up to 10 feet) can be used with double wall construction or larger diameter single wall. Both present their own unique installation challenges, but K-Flex USA said it can provide installation guidelines and recommendations through technical bulletins that give the installer the basic information needed to install closed-cell elastomeric liners efficiently and correctly.

This article originally appeared in the January 2016 issue of SNIPS magazine in a special SPIDA insert. This article and its images were supplied by K-Flex USA.