Document O3br4bN10VgwdRM7M1D8yNow1

434 CHAPTER 21 1949 Guide in balancing the air distribution of the system, a damper should be placed in each leader pipe except one, this latter leader preferably being connected to a room heated at all times, such as a living room. In a gravity circulating system, the ratio of stack to leader area is quite ' F. Noother connection besidethat ,to furnace. : : R. Baseboard register. , . ... G. Cleanout frame and door, airtight. "8. Distribute pipes equally around bonnet. ;;H. Smokepipe,endflushwitninneraurfaceofflue. T. .Floor.register. ' . ~ I. Draft door. U. Return,air face. ' J. Use flue thimble. - V. Pannmgxiinder joist: ' K. Casing body. . . W. Transition collar. Ls Casing hood or bonnet, top of all leader collars oh X. Round return pipe. ' - same level. .. Y. Transition shoe. ,. U. Round leader, pitch 1 in. perfoot. ' Z. Top of shoe at'casing not'above grate level: From N.W.A.H.&A.C.Ajs9n. Standard Code Application Manual. ,, * important, although little-is gained by providing wall stacks with areas in excess of 75 per cent of their connectedleader pipe area. In mostcases a 31 in. X 12 in. stack is the largest which can be installed in normal;wall construction. Hence, any room having.a heatiloss much in excess of 9000 Btu per hr, will require twOionmore stacks,- or one oversized stack built into "a 6 in. studding space; providing the -design register. temperature is to be retained at the value of 175 F as recommended. Gravity Warm Air Systems 435 Registers used for discharging warm air into, rooms should have a net area not less, than the area of the leader pipe to which the register is at tached. First story registers should be connected through boot and register box extensions having areas at ieast equal' to leader area?. Upper story registers should be of the same width as the wall stack, and should be placed-' either in the baseboard or sidewall, preferably without offsets. First story registers may be of the'baseboard or floor type, with the former location'- preferred. High sidewall registers in gravity systems deliver more warm air into the room than do baseboard registers, but most of the additional air merely results in high temperatures at the ceiling. > I ; RETURN AIR GRILLES, DUCTS, AND CONNECTIONS , . ; The placement and number of return grilles will depend upon the-size, details, and exposure of the house. Small compactly built houses may In adequately served by a single return grille effectively placed in the central hall. It is usually desirable to have two or more returns, provided that in two-story residences one return is placed to effectively receive the return . air at the foot of the stairs. A return air connection must be carried to any room whose floor level is below that of adjacent rooms! " .. The return air grilles should have free areas at least equal to the ducts to which they connect and should be installed in the floor, or in the base board with the top edge of the grille not more than about 14 in. above the floor line. Frictional resistance in the return air system is as detrimental as is resistance in the warm-air system, so that care should be exercised in locating return air grilles which require long return ducts. . Where a.divided system of two, or more returns is used, the grilles must be placed to serve the maximum area of cold wall or windows. Thus, in rooms having only small windows the grilles can be brought as close to the furnace as possible, but if the room has large window exposure the grille should be located near the exposure. The frictional resistance of thelong ducts used in parallel with short return ducts must be reduced to com pensate for the length. Return ducts from upstairs rooms may be neces sary in spaces which are closed off from the rest of the house or which have much outdoor exposure. Return grilles on different floor levels should not be connected to.the same vertical return duct. The ducts'through which air is returned to the furnace should be designed to minimize resistance to air flow. They should.be of ample area, in excess of the total area of warm-air pipes, and should be streamlined. Hori- . zontal ducts should pitch at least in. per foot downward, toward the furnace, avoiding fittings which would require lifting of the return air after the duct has passed under some obstacle. Ducts returning air to.the furnace should avoid-heat sources which' . tend to reheat the return air. If the duct must be run over the top of the furnace, or above the vent pipe from the furnace, insulation should be inter-, posed between the heat source and the duct. Circulation of air is facilitated if the air can slide down a pipe inclined at approximately 45 deg and into a furnace shoe connection having a cross-. sectional area equal to that of the pipe. The top of the return shoe should enter the casing below the level of the grate in the case of a coal furnace, and not more than 14 in. above the floor in the case of oil"or gas furnaces. In order to accomplish this the shoe is made wide.