Document JD2yyo2kvjYqBwNGVgNMmJvv

390 CHAPTER 21 1946 Guide In a gravity circulating system, the ratio of stack to leader area is quite important, although little is gained by providing wall stacks with areas in excess of 75 per cent of their connected leader pipe area. In most cases a 3J4 in- X 12 in. stack is the largest which can be installed in normal wall construction. Hence, any room having a heat loss much in excess of 9000 Btu per hour, will require two or more 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. Y-* ' - Gravity Warm Air Systems 391 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. return air ducts, grilles, and shoe connections 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 stream lined. Horizontal 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. 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- Fig. 1. A Sectional View of a Typical Plant Showing Good Installation Practice3 A. House chimney, no bends nor offsets, B. Top of chimney at least 2 feet above ridge of roof. C. Flue lining, fireclay. D. All joints air tight. E. At least 8 in. brick. F. No other connection beside that to furnace. G. Cleanout frame and door, airtight. H. Smoke pipe, end flush with inner surface of flue. I. Draft door. J. Use flue thimble. L. Casing hood or bonnet, top of alfleader collars on same level. K. Casing body. M. Round leader, pitch 1 in. per foot. NJ Sleeve with air space around leader where nagging through wall. O.- Dampers in all leaders. P. Transition fittings. - Q. Rectangular wall stack. R. Baseboard register. S. Distribute pipes equally around bonnet. T. Floor register. U. Return air face. V. Panning under joist. W. Transition collar. X. Round return pipe. Y. Transition shoe. Z. Top of shoe at casing not above grate level. From N.W.A.H.&A.C. Assn. Standard Code Application Manual. 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 attached., First story registers should be connected through boot and register box extensions having areas at least equal to leader areas. 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. Stcnr^ ujf Register jg0j*3 r FG HI Fig. 2. Typical Warm Air Boots 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. The placement and number of return grilles will depend upon the size, details, and exposure of the house. Small compactly built houses may be 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. "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 grille 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 the . long ducts used in parallel with short return ducts must be reduced to compensate for the length. Return ducts from upstairs rooms may be.