23 31 00 HVAC Ducts and Casings
23 31 16 Nonmetal Ducts
23 31 13 Metal Ducts 23 31 13.13 Rectangular Metal Ducts 23 31 13.16 Round and Flat-Oval Spiral Ducts 23 31 13.19 Metal Duct Fittings 23 31 16 Nonmetal Ducts 23 31 16.13 Fibrous-Glass Ducts 23 31 16.16 Thermoset Fiberglass-Reinforced Plastic Ducts 23 31 16.19 PVC Ducts 23 31 16.26 Concrete Ducts 23 31 19 HVAC Casings