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Y <br />Side seams shall be locked seams. All joints shall be either seamed or lapped <br />not less than 12 in. Such joints shall be match- beaded or beaded. All pipes and <br />fittings shall be properly secured to ceiling or joist. <br />(b) All warm air pipes in the basement should preferably have an upward <br />pitch of 1 in. per running foot, but in no case ehould the pitch be downwards <br />from bonnet to boot. <br />(c) All warm air pipes, in the basement shall be provided with dampers <br />supported on both sides and as near the casing as possible. <br />(d) Nhere warm air pipes pass through a masonry wall a metal thimble <br />shall be provided, having a diameter at least 1 in. greater than the pipe, and <br />pipe supported in such a manner that the air space is uniform on all sides. The <br />air space may be filled with non - combustible insulation. <br />(e) where warm air pipes pass through or into unheated spaces separated <br />from the furnace room, they shall be insulated with not less than three layers <br />of air cell asbestos paper or installed with an equivalent insulating substitute. <br />(f) All applicable provisions in the Underwriters' Standards shall be <br />followed. (See Section 310 "warm Air Supply Ducts. ") <br />Section 6. Wall Stacks or Risers. <br />(a) warm air risers shall be constructed entirely of non - combustible <br />material equivalent in structural strength and durability to the following: <br />Width Minimum Minimum Thickness <br />Inches ;" ?eight of Tin of Galvanized Iron <br />14 or less IC (107 lb.) 30 U. S. gauge <br />over 14 IX (135 lb.) 28 U. S. gauge <br />(b) All applicable provisions in the Underwriters' Standards shall <br />be followed. (See Section 310 ":'larm Air supply Ducts" which give provisions for <br />both single -wall and double -wall construction.) <br />(c) All risers shall be braced in a proper manner so as not to obstruct <br />the flow of air but to retain the full capacity throughout. <br />Section 7 Registers. <br />(a) When the baseboard or wall registers are used, they shall be <br />properly sealed to the stack head in such a manner as to prevent any leakage of <br />air between the head and the register. <br />MW <br />