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Heating Ventilating Air Conditioning Guide 1938 this type of corrosion than the ferrous metals, and considerable attention is now being given to corrosion-resistant linings for ferrous pipe. Castiron pipe, sometimes alloyed with other metals, also deserves con sideration. PROBLEMS IN PRACTICE 1 What is the meaning of IPS brass pipe? It means that the brass pipe has the same external diameter as steel pipe in the same nominal pipe sue and that the wall thickness is sufficient to allow cutting of threads for use with standard size threaded fittings. 2 Why is thin-walled copper pipe made up with sweated joints? If the pipe were threaded it would be necessary to use at least standard-weight wall thickness on account of the metal removed in threading. Flared ends with coupling nuts may be used, but this construction is expensive and hard to keep tight. 3 How are pipes designated in diameters of 12 in. and less? By weight and nominal size, referring to the approximate inside diameter. 4 How are pipe sizes designated in diameters of 14 in. and more? By wall thickness and outside diameter. 5 Why are expansion joints required in steam pipes? To care for the change in length of the line brought about by a change in temperature. 6 What devices are used for taking up expansion? Expansion joints, swivel joints, and the inherent flexibility of the pipe itself. 7 Where are swivel joints principally used? In branch connections to radiators, and in the risers of multi-story buildings where they are installed between the floor joists. 8 # Name three grades of American Standard screwed pipe fittings. 125-lb cast-iron, 150-Ib malleable iron, and 250-lb cast-iron. 9 In what sizes are American Standard cast-iron flanges and flanged fittings for 25-lb saturated steam pressure made? \ In nominal sizes from 4 in. to 72 in., inclusive. 10 What fittings are generally used for threaded connections in low pressure heating systems? Cast-iron. 376 Chapter 19 GRAVITY WARM AIR FURNACE SYSTEMS Design Procedure, Estimating Heating Requirements, Leader Pipe Sizes, Proportioning Wall Stacks, Register Selections, Recirculating Ducts and Grilles, Furnace Return Connection, Furnace Capacity, Examples, Booster Fans WARM air heating systems of the gravity type are described in this chapter1, and those of the mechanical type are described in Chapter 20. In the gravity type, the motive head producing flow depends upon the difference in weight between the heated air leaving the top of the casing and the cooled air entering the bottom of the casing, while in the mechanical type a fan may supply all or part of the motive head. Booster fans are often used in conjunction with gravity-designed systems to increase air circulation. In general, a warm-air furnace heating plant consists of a fuel-burning furnace or heater, enclosed in a casing of sheet metal or brick, which is placed in the basement of the building. The heated air, taken from the top or sides near the top of the furnace casing, is distributed to the various rooms of the building through sheet metal warm-air pipes. The warm-air pipes in the basement are known as leaders, and the vertical warm-air pipes which are run in the inside partitions of the building are called stacks. The heated air is finally discharged into the rooms through registers which are set in register boxes placed either in the floor or in the side wall, usually at or near the baseboard. The air supply to the furnace may be taken (1) entirely from inside the building through one or more recirculating ducts, (2) entirely from outside the building, in which case no air is recirculated, or (3) through a combination of the inside and the outside air supply systems. DESIGN PROCEDURE The design of a furnace heating system involves the determination of the following items: 1. Heat loss in Btu from each room in the building. 2. Area and diameter in inches of warm-air pipes in basement (known as leaders). 3. Area and dimensions in inches of vertical pipes (known as wall stacks). 4. Free and gross area and dimensions in inches of warm-air registers. 5. Area and dimensions of recirculating or outside air ducts, in inches. 6. Free and gross area and dimensions in inches of recirculating registers. ?l`U'tmJP'i}cUns12u'*f t(1.e engineering data which follow are from University of Illinois, Engineering fA?- C?. "W"illard. A. P. Kratz, V. S. 1D1a!y.!8a8n-d 1S8.9 Kaonndzo2.46; Warm Air Furnaces and Heating Systems, by 377