The most common method of heating water for the range boiler is by use of the water-back or water-front of the kitchen range. The water-back is a hollow cast-iron piece that is made to take the place of the back fire-box lining of the range. In some ranges the heater occupies the front of the fire-box instead of the back, in which case the heater becomes the water-front.

The arrangement of pipes connecting the source of water supply with the boiler is such that cold water is constantly supplied to the tank as the hot water is drawn. If no water is drawn from the tank, it will continue to circulate through the tank and heater, the water becoming constantly hotter.

The connecting pipes are usually of iron but sometimes pipes of copper or brass are used. The joints should be reamed to remove the burr that is formed in cutting. The angles should be 45-degree bends or better still 90-degree bends in connecting the heater with the tank so as to cut down the amount of friction as much as possible.

In Fig. 113 is shown a standard range boiler connected to the range. The water is brought into the top of the tank through the pipe a-a, and passing through it enters the water-back by means of the pipe b. After passing through the water-back the water again enters the tank through the pipes c and d, as indicated by the arrow. The flow pipe (carrying the out-going water) from the water-back may be connected with the tank at e, as shown dotted or in some cases the connections are made at both places. The velocity of circulation depends on the vertical height of the column of hot water and the greater height will, therefore, improve the circulation and thus increase the efficiency of the heater. The circulation of the water through the tank and heater is produced by its change in weight as the water is heated. As the hot water comes from the water-back it rises in the pipe because it is lighter in weight than the cooler water of the tank. In the case of the pipe shown dotted in Fig. 113 the longer vertical rise will give a greater upward velocity of the hot water and consequently a better circulation through the entire circuit.

Fig. 113. - A common method of connecting the range boiler to the water-back.

The construction of the water-back is shown in the small drawing. The connections are made at b and c as before. A division plate in the water-back causes the water flowing in at b to follow the length of the heater at the bottom and return at the top as indicated by the arrow, when it is discharged at C.

The hottest water is always at the top of the tank and the temperature grades uniformly from the hottest at the top to the coolest at the bottom. The reason for extending the pipe a so far down into the tank is that the cold water may not mingle with the hot water and reduce its temperature on entering the tank. Near the top of the pipe a is a small hole / that is intended to prevent the water from being siphoned from the tank in case a vacuum is formed in the cold-water pipe. In this arrangement the water enters and leaves at the top of the tank. In case the supply is shut off at any time the tank is left almost full of water, because the siphoning effect cannot extend below the small hole /.