Ans. 7.4 sq. ft.

3. A hot-water storage tank has a steam coil consisting of 30 linear feet of 1-inch iron pipe. It is desired to connect a coal-burning heater for summer use, which shall have the same capacity. Steam at 5 pounds' pressure is used, and the water is raised from 40 to 180 degrees. How many square feet of grate surface are required?

Fig. 84. Storage Tank Heated by Steam Coil in Winter; Cross-Connected to.

Coal Heater in Summer.

Ans. 5.9 sq. ft.

4. A hotel has 30 bathtubs, which are used three times apiece between the hours of seven and nine in the morning. The hot-water system has a storage tank of 400 gallons. Allowing 20 gallons per bath, and starting with the tank full of hot water, how many square feet of grate surface will be required to heat the additional quantity of water within the stated time, if the tempearture is raised from 50 to 130 degrees? Ans. 11.6 sq. ft.

If steam at 10 pounds' pressure is used instead of the heater, how many square feet of heating coil will be required?

Ans. 15.3 sq. ft.

The ratio of transmission of heat from steam to water through iron pipe, increases with the temperature difference, from 150 B.T.U.

per square foot, per hour per degree for 100° difference, to 228

B.T.U. for 125° difference. The relative condensing power of submerged iron, brass, and copper pipe is about as 2, 4, and 5, respectively.

Within the range of water temperatures usual in practice and with steam at ordinary pressure, we may safely place the condensing power of iron, brass, and copper pipe in even tenths, .2, .4, and .5 pounds per hour, per square foot, per degree difference between the steam and mean temperature of the water. With these values, the latent heat of steam, say 960, should be used in converting heat units, found as in preceding examples, into "pounds" of steam. Having this latter, the process of finding the coil surface would be: multiply the temperature difference by the constant .2, .4, or .5, according to the kind of pipe coil to be used, and divide the "pounds" of steam by the product so obtained. The result will be coil surface in square feet, which may be converted into lineal feet by multiplying by 2.9 for 1-inch pipe; by 2.3 for 1 1/4 -inch pipe; by 2. for 1 1/2-inch pipe, and by 1.6 for 2-inch pipe. As in some of the previous examples three feet of 1-inch pipe are generally taken as one square foot. Sometimes a storage tank is connected with a steam-heating system for winter use, and cross-connected with a coal-burning heater for summer use when steam is not available. Such an arrangement is shown in Fig. 84. A cross-connection for the same purpose is often made to the fire-pot of the house-warming heater, as indicated in Fig. 85. A drain at the lowest point is essential, but so deep a dip as shown is not necessary.

Fig. 86. Cross-Connection of Storage Tank to Firepot of Furnace.

Pig. 86. Temperature Regulator Attached to Coal Heater..

Fig. 87. Temperature Regulator Connected to Steam Coil..

Fig. 88. Complete Layout for Hot-Water Storage System Using Ruud Automatic Gas Heater.

Temperature Regulation. Hot-water storage tanks havings special heaters or steam coils, should Be provided with some means for regulating the temperature of the water. Fig. 86 shows a simple form attached to a coal-burning heater. An outer shell is connected with the circulation pipe as shown in Fig. 86. An inner chamber connects with a space below a flexible rubber diaphragm in a separate case adapted to operate the draft lever.

Fig. 89. Typical Automatic Gas Heaters for Instantaneous Hot-Water Service Left - Humphrey Heater; Right - Ruud Heater..

A form of regulator for use with a steam coil is shown in Fig. 87. This consists of a rod made up of two metals having different coefficients of expansion, and so arranged that the difference in expansion will produce sufficient movement to open a small valve when the water reaches a given temperature. This allows water pressure from the street main with which it is connected, to flow into a chamber above a rubber diaphragm, thus closing the steam supply to the coil. When the water cools, the rod contracts, and the pressure is released above the diaphragm, the valve opening to admit steam again.

Return-circulation is-provided in these installations in the way already described, being even more essential than in small jobs with shorter runs and fewer fixtures; yet one would think that the great number of fixtures served would insure at least one or another being in constant use, and thus keep warm water in the main lines without special provision for the purpose.

In cottages with no bath and with small culinary requirements, to Range Boiler Controlled by a 30-gallon reservoir is sufficient. Not less than 40 gallons should be employed for a bathroom job. The capacity of the average stove heater is even too great for 40 gallons' storage unless there is liberal use of hot water; but where gas is used and the water heating independent of the cooking heat, as it generally is, the temperature can be regulated to suit. A storage capacity of 52 gallons or more is usual for large residences.

Fig. 90. Crane Gas Heater Connected Thermostatic Valve.

Fig. 91. "Lawson" Combination Gas Heater and Range Boiler Thermostatic Control Valve at Left. Courtesy of Crane Company, Chicago.

Gas Heaters. There are gas heaters provided with thermostatic or pressure mechanism by which the hot service is taken care of automatically. The latter of these are simply connected in the line in a convenient place, and operated by a differential valve. Their appearance is shown in Fig. 89. Simply opening any hot-water faucet reduces the pressure, and the gas is thereby turned on full as long as water is drawn. A pilot light ignites it, and the supply is heated as fast as it passes through the copper coils of the heater. No storage capacity is required by this form. In another form, shown in Fig. 90, the heater is controlled by a thermostatic valve projecting into the regular reservoir used with it. When the water in the reservoir is heated to the desired temperature, the gas supply is reduced or cut off. In Fig. 91 is shown in part section the "Lawson" combination gas heater and range boiler. This is a very reliable heater and is very well designed. The copper-tube coil forms the direct heating surface, having water connections at both top and bottom of the boiler. The thermostatic valve shown at the left regulates the gas consumption. Drawing water from the hot faucets lowers the temperature in the reservoir through the cooling influence of the incoming water, and the thermostatic principle is again made to serve in opening the gas-valve until the water is heated to the desired temperature.

Fig. 92. Instantaneous Gas Heater Connected to Gas Supply Pipe and Operated Directly in Bathroom. Courtesy of The Humphrey Company, Kalamazoo, Michigan..

There are other arrangements consisting essentially of an encased copper coil, above a gas-burner, connected to a standard reservoir at top and bottom. In these, the gas is turned on and regulated by hand as nearly as possible to suit the needs.

Instantaneous water-heaters, operated by gas or gasoline, and placed in proximity to the fixtures served, as shown in Fig. 92, so as to deliver the heated water directly, are in general use where local conditions favor them. These have no storage capacity. A sectional view of Fig. 92 is shown in Fig. 93. In this heater, the water is not exposed directly to the heated air and gases, and water so heated is suitable for use for any purpose so far as the method of heating is concerned. The purposes for which water heated in contact with the gases of combustion may be used is limited. Other heaters of this class offer admirable means for the water to take up the heat generated by the gas. All of these special means of heating water - especially those not conforming to the plumber's regular routine - are best understood and judged by a close study of the literature supplied by the makers.