122 6

THEORY AND PRACTICE OF ENGINEERING.

Book II.

iron pipes are substituted for the round, those giving out more heat: hermetically closedtubes are found useful in conveying the warm water to a greater distance; and then asmaller diameter of tube may be adopted, as the water may be raised to a temperatureconsiderably above the boiling point: by the use of ascending and descending pipes, watermay be made to circulate to any height; and it is calculated that a fire-grate of about 12superficial feet, with a properly constructed boiler, consuming a bushel of coals per hour,is sufficient to heat a moderate dwelling ; the boiler having a bottom surface, in thisinstance, of 48 feet, or four times the area of the grate, and alx>ut 32 feet of side Hue. Thequantity of pipe to be heated must regulate the size of the boiler, and as each cubicfoot of water evaporated per hour requires 4 superficial feet, we may ascertain therequisite proportions for a boiler of a hot-water apparatus. Supposing the latent heatof steam 1000°, we shall find that the size of a boiler which would evaporate a cubefoot of water, at the temperature of 52°, into steam, would supply sufficient heat to 232feet of 4-inch pipe, and maintain its temperature 140° above that of the surroundingatmosphere.

When the difference between the temperature of the pipe and the air is 125°, it hasbeen found that a foot of 4-inch pipe will heat 200 cubic feet of air 1° per minute; andwhen the pipes are 146° hotter than the air around them, the water within them loses1 ° of heat per minute.

Fig. 1925-

section OP CALORIFERB,

Where many stories of a building are to bewarmed the boiler and furnace are placed on

f)F3

Fig. 1926. valves.

the lower story or basement, from which rises a flow-pipe to a warm-water-box placed atthe top of the house ; from this another pipe supplies a small calorifere or metal box con-taining water, one of which is placed in every room intended to be warmed: and afterpassing through all, the water returns to the boiler to be again heated; a regular circulationis thus kept up ; the cold water, being heavier than that warmed, falls to the bottom of thepipe, and forces up the latter.

Each 100 feet of 4-inch pipe, containing 544 pounds of water, will require 14 pounds