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DocuSign Envelope ID: 9826C043- 4C32- 49CD- A4CC- DC28ABAB7CE7 <br />SECTION 239000 - METAL DUCTS <br />G. Round ducts may be substituted for rectangular ducts if sized in accordance with ASHRAE table of <br />equivalent rectangular and round ducts, with approval of Engineer. No variation of duct configuration <br />or sizes permitted except by written permission of the Architect /Engineer. <br />H. Increase duct sizes gradually, not exceeding 15 degrees divergence wherever possible. Divergence <br />upstream of equipment shall not exceed 30 degrees; convergence downstream shall not exceed 45 <br />degrees. <br />9.7 KITCHEN HOOD EXHAUST DUCT CONSTRUCTION <br />A. In concealed locations use minimum 16 gauge black steel or minimum 18 gauge stainless steel with <br />all joints welded liquid tight or prefabricated grease duct, Underwriters Laboratory, Inc listed with <br />aluminized steel shell <br />B. Note: Factory prefabricated duct may still require a 2 -hr fire rated enclosure or fire stop insulation <br />where concealed and serving a Type I hood (grease vapors or smoke). As of the date of the updated <br />version of this specification section, grease duct manufacturers do not have a product that is UL <br />listed for grease vapor and smoke application. <br />C. In exposed areas, use 18 gauge or heavier stainless steel with a number 3 finish and with all joints <br />welded liquid tight or prefabricated Underwriters Laboratory, Inc listed duct with stainless steel shell. <br />Grind and polish all welded joints and seams to a number 3 finish. <br />D. Provide expanded take -offs for branch duct connections or 45 degree entry fittings. Square edge 90 <br />degree take -off fittings or straight taps will not be accepted. <br />E. Use elbows and tees with a center line radius to width or diameter ratio of 1.5 wherever space <br />permits shall be used wherever possible. Shorter radius elbows may be used in areas with limited <br />space with prior approval of the Architect /Engineer. <br />F. No turning vanes may be used in kitchen exhaust duct. <br />G. Supporting steel and hangers shall not be lighter than the duct gauge. <br />9.8 DISHWASHER EXHAUST DUCT CONSTRUCTION <br />A. Fabricate and install ductwork in sizes indicated on the drawings and in accordance with SMACNA <br />recommendations, except as indicated below. <br />B. Use 18 gauge or heavier stainless steel with all seams and joints welded and ground smooth. In <br />exposed areas, joints and seams to be polished to a #3 finish (minimum). <br />C. Use elbows and tees as specified for the appropriate duct pressure class. <br />D. Provide expanded take -offs for branch duct connections or 45 degree entry fittings. Square edge 90 <br />degree take -off fittings or straight taps will not be accepted. <br />9.9 FUME EXHAUST DUCT CONSTRUCTION <br />A. Use PVC coated steel or stainless steel duct and fittings. Use stainless steel for all exposed <br />installations below suspended ceilings. <br />B. Use 316 stainless steel for flanged gasketed connections. <br />C. Use 18 gauge or heavier 316L stainless steel sheet for externally welded ductwork. Grind and polish <br />joints and seams to a #3 finish minimum. <br />9.10 DUCT SEALANT <br />A. Manufacturer: 3M 800, 3M 900, H.B. Fuller /Foster, Hardcast, Hardcast Peal & Seal, Lockformer cold <br />sealant, Mon -Eco Industries, United Sheet Metal, or approved equal. Silicone sealants are not <br />allowed in any type of ductwork installation. <br />B. Install sealants in strict accordance with manufacturer's recommendations, paying special attention to <br />temperature limitations. Allow sealant to fully cure before pressure testing of ductwork, or before <br />startup of air handling systems. <br />9.11 GASKETS <br />A. 2 inch pressure class and lower: Soft neoprene or butyl gaskets in combination with duct sealant for <br />flanged joints. <br />B. 3 inch pressure class and higher: Butyl gaskets. <br />C. FUME HOOD EXHAUST; Butyl gaskets. <br />EXECUTION <br />9.12 DUCT INSTALLATION <br />A. Drawing plans, schematics, and diagrams indicate general location and arrangement of duct system. <br />Indicated duct locations, configurations, and arrangements were used to size ducts and calculate <br />friction loss for air - handling equipment sizing and for other design considerations. Install duct <br />systems as indicated unless deviations to layout are approved by Designer prior to fabrication. <br />B. Take field measurements to verify duct routing and coordination with all trades prior to fabrication. <br />C. Install ducts according to SMACNA's "HVAC Duct Construction Standards - Metal and Flexible" <br />unless otherwise indicated. <br />D. Install round ducts in maximum practical lengths. <br />E. Install ducts with fewest possible joints. <br />F. Install factory- or shop- fabricated fittings for changes in direction, size, and shape and for branch <br />connections. <br />G. Unless otherwise indicated, install ducts vertically and horizontally, and parallel and perpendicular to <br />building lines. <br />Reece, Noland & McElrath, Inc. 239000-3 Orange County Board of Elections <br />Orange Co., NC 05/04/18 <br />