The siphon hole, as it is termed, should be turned in the direction opposite the eccentric hole, which is for the hot-water exit, so that the stream of cold water which issues there when water is coming into the reservoir will not cut across and interfere with the hot service which is always leaving the reservoir at the same time. If the delivery were placed nearest the side hole, hot water from the stove would have to pass around it in order to reach the exit. Delivering the cold through a pipe passing down through the volume of hot water is no material retardation of the heating process. The heat thus absorbed by the cold delivery is simply that much aid to the ultimate purpose. This cannot be said of the siphon-hole jet when directed across the hot exit or in its direction.

The object in putting the siphon-hole near the upper head is to avoid siphoning more water than necessary, as the waste tubes of stop and waste cocks are generally left open - not connected to drains, and often not even discharging where the waste can be left to take care of itself. Moreover, it is a waste of the stored hot water to siphon out several inches from the hottest point.

Fig. 81. Pipe Connections to Heater and Fixtures. Hot Service and Circulating Pipe Shown by Dotted Lines. Return Circulation Connected to Bottom Pipe in Water-Back..

Care should be taken not to have the hot connection extend into the upper head below the inner surface, as this would form an airspace which could not be filled with water, and thus annoying noise and the formation of steam would be favored, if no other consequence presented itself.

It is essential to keep the water-back or coil filled. Sometimes the supply may be off for a day or so. No water can then be drawn at the regular faucets; and extreme care should be taken not to draw too much from the sediment faucet, as this is the time when temptation to use it is hard to overcome. The reservoir full will keep the level above the side hole for weeks, if none is deliberately drawn out. The height of the water can be told by tapping on the shell, and in no case should it be allowed to fall below the side opening; neither will it do to empty the reservoir and use the fire with the back empty. Either keep water in the reservoir in cases of emergency, or remove the water heater altogether and substitute a tile back until regular water supply can be had. A reservoir can be replenished with a pail and funnel, by hand, by loosening one of the top connections.

Fig. 82. Horizontal Hot Water Storage Reservoir with Steam Coil of Brass Pipe for Heating Used Where Steam Pressure is Constantly Maintained..

In apartment or other houses where steam pressure is constantly maintained, the whole plumbing system is usually supplied with hot water through the medium of a reservoir provided with steam coil of iron, brass, or copper pipe, as shown in Figs. 82 and 83. The trombone coil, illustrated in Fig. 82, can be used only on horizontal tanks; it would not drain in any other position. The condensed steam is wasted into the sewer, delivered to a hot well, or returned by steam trap.

The efficiency of a steam coil when surrounded by water is much greater than when placed in the air. An iron pipe will give off about 200 thermal units per square foot of surface per hour for each degree difference in temperature between the steam and the surrounding water. This is assuming that the water is circulating through the heater so that it moves over the coil at a moderate velocity. The condensing power of galvanized pipe is very nearly the same as that of plain iron, its coating being an alloy and not pure zinc as is generally supposed. The ratio of absorption decreases as the temperature of the water approaches that of the steam surface. In assuming the temperature of the water, take the average between that at the inlet and that at the outlet.

Example. Find the heating surface required in an iron coil to heat 100 gallons of water per hour from 38 degrees to 190 degrees, with steam at 5 pounds' pressure?

Water to be heated = 100 X 8.3 = 830 pounds.

Rise in temperature = 190 - 38 - 152 degrees.

Average temperature of water in contact with the coils

= 190 + 38 / 2 = 114 degrees

Temperature of steam at 5 pounds' pressure = 228° approximately (actually 227.964°).

The required B. T. U. per hour =830X152 = 126,160.

Difference between the average temperature of the water and the temperature of the steam = 228 - 114 = 114 degrees.

B. T. U. given up to the water per square foot of surface per hour = 114 X 200 = 22,800. Therefore,

Number of feet of heating surface required = 126,160 ÷ 22,800 ==5.5 square feet of surface or 12.6 lineal feet of 1 1/4-inch, or 16 lineal feet of 1-inch pipe.

Fig. 83. Vertical Storage Reservoir with Steam Coil of Iron, Brass, or Copper Pipe for Heating, Used Where Steam Pres- sure is Constantly Maintained..

Examples For Practice

1. How many linear feet of 1-inch iron pipe will be required to heat 150 gallons of water per hour from 40 to 200 degrees, with steam at 20 pounds' pressure? Ans. 21.3 feet.

2. How many square feet of grate surface will be required in a heater to heat 300 gallons of water per hour from 50 to 170 degrees?