Galvanized Steel Ducts
This information reflects our best understanding of product composition in 2015.
Galvanized steel ducts are the most frequently used duct material for heating, ventilation, and air conditioning (HVAC) systems in commercial and institutional buildings. Galvanized steel ducts may come in round, rectangular, or oval shapes of...
Galvanized steel ducts are the most frequently used duct material for heating, ventilation, and air conditioning (HVAC) systems in commercial and institutional buildings. Galvanized steel ducts may come in round, rectangular, or oval shapes of varying sizes depending upon the application. Galvanized coatings are applied to steel sheets through a hot dip in a 99% pure zinc bath, which reacts with the steel sheet surface to form a coating which protects the steel from corrosion. The HVAC Duct Construction Standards for metal and flexible state that duct work will conform to ASTM A653 and ASTM924 standards for G-60 coated galvanized steel of lockforming grade (also known as commercial steel (CS)), unless otherwise specified. When a CS type is not specified, ASTM A653 recommends furnishing to CS type B. The G in G60 refers to the galvanized (zinc) coating, while the number refers to the weight of zinc on the surface of the steel in inch-pound units. The most commonly used galvanized duct work conforms to G60 or G90. G60 is used commonly for dry indoor ducts while G90 is the minimum requirement for use in any outdoor exposure or wet indoor application. Therefore, most specifications refer to galvanized steel conforming to G90 standards. Ductwork is typically available in 18-28 gauge sizes, but gauges 22-28, especially 26, appear to be the most commonly used. Therefore, this CP describes a 26 gauge G90 galvanzied steel duct conforming to ASTM A653.