Double-Wall, Round Duct

McGill AirFlow’s double-wall, round duct is fabricated to exacting tolerances that make it easy to assemble and essentially leak free. This insulated duct provides excellent acoustical and thermal control with the efficient airflow performance of single-wall round duct. Three standard types of double-wall, round duct are available: spiral lockseam (ACOUSTI-k27®), spiral lockseam with a standing rib (UNI-RIB-k27®), and longitudinal seam (Longitudinal Seam-k27®).

Spiral lockseam duct is constructed with an interlocking helical seam that runs the length of the duct’s outer pressure shell. This seam increases the duct’s structural strength and rigidity so that it can be used in lighter gauges than rectangular or longitudinal seam duct, making it less expensive, easier to handle, and easier to install. Another factor which makes spiral lockseam duct economical is that it can be fabricated in lengths of 20 feet or greater. These longer sections of duct mean fewer joints and faster installation.

Spiral lockseam duct is available with a standing rib on the outer pressure shell. This external stiffening rib gives the duct strength and rigidity equal to that of heavier gauges of standard spiral lockseam duct.

Longitudinal seam duct is available for applications that require very heavy gauges or large diameters. The longitudinal seam of the duct’s outer pressure shell is solid welded.

Double-Wall, Round Duct
Available Sizes, Materials, and Thicknesses

(1) Standard insulation density is 1.0 pcf.

(2) Except as noted, McGill AirFlow double-wall, round duct and fittings are available with the following outer shell dimensions: 5-inch through 15-inch diameters in 1/2-inch-diameter increments, 16-inch through 38-inch diameters in 1-inch-diameter increments, and 40-inch through 90-inch diameters in 2-inch-diameter increments. Standard fitting liners are solid metal. Standard insulation is fiberglass.

(3) Standard lengths of round ACOUSTI-k27 and UNI-RIB-k27 duct are 10, 12, and 20 feet; longer lengths are available. Standard lengths of round Longitudinal Seam k-27 duct are 5 and 6 feet.

(4) Double-wall, round duct and fittings are also available in carbon steel, paintable galvanized steel, types 304 and 316 stainless steel, and type 3003-H14 aluminum.

(5) UNI-COAT® double-wall, round duct and fittings (polyvinyl-chloride-coated galvanized steel) are available on special order.

(6) Aluminum double-wall, round duct and fittings are available in larger diameters and greater metal thicknesses on special order.

(7) Round Longitudinal Seam-k27 duct is available with inner liners less than 8 inches in diameter on special order.

(8) SilverGuard™ double-wall, round duct and fittings (pre-coated with an antimicrobial) are available on special order.

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An enterprise of United McGill Corporation—Family owned and operated since 1951

Unless otherwise noted, all (™) trademarks and (®) registered trademarks are property of United McGill Corporation.