Document mm7bge3n3dkJLpExBBjnnNDyb

408 CHAPTER 22 . : , h .1948 Guide Table 1. WarmAirDuct System Combinations of Parts Selected as Standard .Combi nation No. .. Stack ' 1 Size In. Branch Pipe Size, In. Round Rec tangular . Base. BOARD orLow Sidewall . Register Size, In. (See Figs. 1 and 2) High Sidewall For throws For throws less than more than 13 ft 13 ft - Floor . 'Regis-.: . TERS Required Increase ' in Width of Trunk Duct, In. . . 1 : 2 ` 3 ' ,,4 5 '6 7 . V., ;8 9 41 - 10 x 3M ': V 6 4x8 10 x -6 10 x 6 10 x 4 8 x 10 ,i 42 10 x 3J 6 4x8 10 x 6 10x6 10 X 4 8 x 10 2 43- 12x3M 7- 5x8 12x6 12x6 ,12 x 4 9 x 12a 44 ' U*3X 8 6x8 14x6 14 x 6 14 x 4 9 x 12a or longer 45 10 x 3M , ' 9 !: 8 x 8 (2) 10x6 (2) 10x6 (2) 10x4 10 x 12a (2-Stacks) .or .. or or (1)24x6 (1)24x6 (1) 24 x 4 3 4 6 46 12x3^ 10 (2-Stacks) 10 x 8 (2) 12 k 6 (2) 12x6 (2) 12x4 12 X 14a or or or (1)30x6 (1)30x6 (1)30x4 ;7 "Use these items only when the building construction or capacity requirements necessitate the use of floor registers. The sixes listed for floor registers correspond to-the standard sizes for gravity warm-air systems, except for the sizes of the floor box collars. The use of standard blind boxes is suggested. of any system to avoid turbulence and' to minimize" resistance. Sharp elbows, angles, arid offsets shbuld be avoided, s Three types of dampers are commonly used.- Volume dampers are1tiseii to completely cut off- or reduce the flow through pipes. Splitter dampers are used where a branch is taken off from a main trunk. . Squeeze dampers axe used for adjusting the volume of air flow and resistance through a given'duct. It is essential that a damper with positive locking device be provided for each main or duct branch. Labels placed on ducts should indicate the room being served. Damper positions . should be marked'for summer, and winter operation, and .to avoid tampering. .'O - Dlict8 ' . V' The ducts may be either round or rectangular .in cross section.. The radii of dbows. should preferably be not less than one and one half times the pi]ph diam'eter.fpr round pip'es,'.dr,the equivalent found pipe size in the chse of rectangular ducts. Warm air ducts passing through cold spaces, dr. .where located in exposed walls, should have ^ to 2 in;-of insulation': Special attention should be given to the problem of.noise elimination! The metal duct connection to and from the furnace casing and fan housing should be! broken by strips of canvas! Motors and mountings riiust be carefully selected for quiet operation-. Electrical conduit and water piping must not be fastened to, nor make contact with fan' housing. Installation pf a fan .directly under a cold air grille is usually np.t recommended.- STANDARD COMBINATIONS OF PARTS . The combinations of parts selected as standard by the National Warm Air Heating and Air Conditioning Association are shown in Tables 1 and 2. A method for selecting these combinations.is indicated in:the following section Simplified Method of Designing Domestic Forced-A ir Systems. Mechanical Warm. Air Systems 409 Table 2. Return-Air Duct System Combinations of Parts Selected as-Standard; Combi nation . No. 1 51 Return-Air Intake Size, In. Base board 2 10x6 Floor 3 6 x 10 . or 4x 14 Riser Size. In. Where Stack is Used in Stud Space Branch Pipe Sue, Ik. Round Rec tangular When Joist Lining IS USEDb Number of Joist Spaces Lined and Minimum Depth op Space Required Required Increase in Width op Trunk Duct (for 8 In. Depth, of duct). In. 4' ' 5 6 7 8 10 x 3Me 6 4x8 1 space of 3 in. depth i 52 10x6 6x 10 10 x 3 or : 4 x 14 6 4x8 1 space of 3 in. ' - 2 . depth 53 12 x 6 6 x 12 .12 x 3Ht ...7 . 5 x_8. 1 space of 4 in.' 3 or. depth 6x 14 54 14 x 6 6 x 14 .14 x 3Md 8 6 x .8 1 space of 5 in. ' 4, depth 55 24 x 6 .. .6x30 Two. .. ... 9' .8x8. 1 space of 6 in. 6 or stacks * depth or 2 spaces 30x6 each of 3 in. depth 10 x 3}4C 56 30 x 6 6x30 Two 10 10 x 8 1 space of 7 in. 7 stacks depth or 2 spaces 12 x 3 of 4 in. depth 57 -- 8x30 12 15 x 8 1 space of 9 in. 11. depth or 2 spaces of 5 in. depth &Use these items only when building construction, or capacities, require the use of floor intakes.-. - The sizes listed correspond to standard sizes for gravity installations, except floor box collars. The use erf standard blind boxes is suggested. bBased on 14 in. space between joists. Use.fuD depth of joist, except when joist depth is less than mini mum depth required, in which case a drop pah must be used. This may occur when two or more return ducts are connected to the same joist space. - elf it is desired to use 14 in. x 3% in. stud space, it makes no difference whether this space has pro truding keys or not. dlf it is desired to use 14 in. x 3&g in. stud space.' the plaster base must be smooth, without any pro trading plaster keys to interfere with the flow of air. SIMPLIFIED METHOD OF DESIGNING DOMESTIC FORCED-AIR SYSTEMS A simplified method fpr selecting the combinations of branches, boots, stacks, arid registers, is giveri in the Code and Manual (Textbook section No. 7) of'the National Warm Air Heating.and Air'Conditioning Associa tion.' In this method the sizes of the'branch dUcts are obtained.from two tables giving their Btu capacities. The proper combination of parts for each branch cari.be determined if the following information is available, a. Location of room, that is, whether on first or second story. b. Actual length of basement duct from bonnet to boot, in feet. : c: Btu loss from room to be heated. d. Equivalent lengths in feet of all fittings and of the register. Fig. 3 shows the values of equivalent lengths of-fittings commonly, used for domestic systems. 1