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Section 3 - Round Pipe. Round pipe shall be constructed of galvanized <br />iron: up to and including 12 in., not lighter than 30 gauge, <br />up to and including 24 in., not lighter than 26 gauge. <br />If slip joints are used, joints shall be stripped with asbestos paper. <br />Section 4 - Rectangular Duct. Rectangular ducts shall be constructed <br />of galvanized iron: <br />up to and including 14 in. wide, not lighter than <br />28 gauge, <br />to 36 in. wide, not lighter than 26 gauge, <br />wider than 36 in., not lighter than 244 gauge. <br />All duct sections 24 in. or wider, and over 48 in. in length, shall be cross <br />broke on top and bottom and shall have standing seams or angle iron braces. All <br />joints shall be S and drive strip, or locked. <br />IQo warm air duct, round or rectangular, shall come in contact with <br />masonry malls. Insulate around all warm air ducts through masonry walls with not <br />less than 1/2 in. of insulation. <br />It is not the intention of this Section to eliminate the use of other <br />satisfactory, non - combustible materials in the construction of ducts. <br />Section 5 - Return Air Liners. Bottoms of all return air joist spaces <br />shall be lined with smooth, air -tight material. All cross bracing should be <br />removed and joists properly reinforced. <br />Section 6 - Insulation of Ducts. All exposed warm air ducts passing <br />through an unheated room shall be insulated with at least 1/2 in. thickness of <br />insulation. eructs located in cold attic spaces, or cold exposed basement spaces, <br />shall be insulated v:ith at least 1 in. thickness of insulation. <br />Section 7 - Duct Supports. All ducts shall be securely suspended from <br />adjacent building members. I\fo nails shall be driven through duct or stack vialls, <br />and no unnecessary holes shall be cut therein. <br />Section 8 - Volume Dampers. Volume dampers of locking type shall be <br />placed in each warm air run. These may be placed near the main trunk, or in the <br />stackhead. <br />Return air ducts and outside air inlet ducts shall be similarly equipped <br />v..ith volume dampers. <br />- 3 - <br />