Document RJJO8jaRRr2Er2oybYKNBMbRv

422 CHAPTER 18 1950 Guide Table 8. Return Air--Carrying Capacity--Btu Serviced Return Air Com bination No. Duct Dia In. Type A Btu per Hr Types B and C Btu per Hr ' Type D Btu per Hr Type E Btu per Hr Type F Btu per Hr RettonAir Com bination No. 31 10 11,300 9,500 7,800 5,000 7,800 31 32 12 16,300 , 13,700 11,300 7,200 11,300 32 33 14 22,200 18,700 15,300 9,800 15,300 33 34 16 29,000 24,400 20,000 12,800 20,000 - 34 35 18 36,700 30,800 25,300 16,200 25,300 35 36 20 45,300 38,000 31,300 20,000 31,300 36 37 22 54,800 46,000 37,800 24,100 37,800 37 38 24 65,200 54,800 45,000 28,700 45,000 38 Design Procedure . The steps to be taken in designing a gravity warm air duct system are: 1. Calculate the heat loss from each room as-explained in Chapters 9,10 and 11. 2. Prepare a layout showing (a) furnace, (f>) chimney connection, (c) warm air registers (whether floor, baseboard or wall), (d) return air grilles. 3. Indicate on each warm air-run (using symbols shown in Fig. 6): (a) whether the room to be heated is on the first or second story, (6) the approximate length of leader pipe in the basement, (c) the number of right angle elbows and equivalent elbows (Table 5) required, including the elbow at the boot connection (see Fig. 2), (d) whether the register is to be located in the floor, in the baseboard, or in the wall. T,p C Same as Type E except that col lar and.shoe are same as tor Type a: Trpt E TlPf F fNote: For Types C, D, E, and F return-air duet systems, reduce the carrying capacities shown in Table 8 by 1 per cent for each 4 ft additional length in the horizontal run. Fiq. 5.` Typical Arrangements op Return,-Aib Duct Systems . Gravity Warm Air Systems 423 . 4. Show the number and proposed locations of return air grilles and the type of return air system (see Fig. 5). 5. From Table 6, for first story, or from Table 7 for second story; select the combit nation numher.for the warm air system which will supply the heat required to each room, with the number of elbows and length of leader pipe previously determined. Then, using the combination number as found, read directly in Tables 1, 2,-or 3 the leader, stack, and register sizes required. 6. From Table 8 select the combination number for the return air system to corre spond with the Btu serviced and the type of return air system. Then from Table 4 select the duct and grille sizes, etc., corresponding to the same combination number. 7. Select a furnace having a register delivery, in Btu per hour, equal to the total heat loss from the structure. Standard work sheets to facilitate design according to the above recom mended procedure, are available from N.W.A.H. & A.C.A. Fig. 6. Typical Basement Line Drawing Design Examples- Examples 1 and 2 will illustrate the use of the tables in selecting warm air and return system sizes. Example 1. For a room which has a heat loss of 22,500 Btu per hr, select the size of first story warm air system. There are three elbows, and the leader is approxi mately 10 ft long. Solution: Since 22,500 Btu is beyond the capacities shown in Table 6, it is neces sary to select two units of 11,250 each. From Table 6 in 10 ft leader column, and in section for three elbows, find 11,400 as nearest capacity which corresponds to Com bination Number 4 in first column. Refer to Combination Number 4 in Table 1 and find that the leader should be 12 in. in diameter, and should be used witha 12 X 14in. floor register or a 13 X 11 in. baseboard register with a 5i in. extension. Example 8. What is the size of a return system of Type D which is to service 35,000 Btu per hr? Solution: From Table 8 find Combination Number 37 which will service 37,800 Btu per hr. Refer to Table 4 to find that Combination Number 37 will require, a 22-in. diameter duct, a shoe area of 420 sq in., a metal grille 18 X 30 in., a duct 42 X 10 in. or 36 X 12 in. If joist lining is used the minimum depth should be 15 in. for two 2-joist spaces 14 in. wide, or 10 in. for three joist spaces.