When the water at a high temperature is drawn from the tap a considerable part of it will instantly vaporize, because of the reduced pressure. If water at a pressure of 25 pounds is drawn from the faucet, the temperature, 258°F., is sufficient to send all of the water instantly into steam. This high temperature will scald at the slightest touch. The water drawn from the faucet will continue to vaporize as it comes into the air until the water in the tank is cooled by the incoming cold water. The only means of relieving the overheated condition is to open the faucet a slight amount and allow a portion of the heated water to be drawn off. It is evident from what has been said of the range boiler that it operates under a variety of conditions. It is first a storage tank in which is accumulated the water, heated from a greater or less period of use of the range. Should the range fire be maintained through the day or night the supply of hot water will be excessive and superheating is the result. If the heater is to be used during short periods of time, the piping should be arranged to produce the best circulation; on the contrary, should the heater be used continuously--as in the case of a furnace coil--a slow circulation through the tank is most to be desired and the piping should be arranged for that purpose. In the use of furnace heaters, superheating is likely to occur during cold weather when a hot fire must be used over a long period of time. In order to conserve the heat accumulated under such conditions a hot-water radiator is frequently connected with the range boiler through which to dispose of the excess heat. This radiator may be placed in any desired position and so connected by a valve as to discontinue its use at any time. [Illustration: FIG. 120.--The range boiler connections when a furnace coil is used for hot-water heating.] =Furnace Hot-water Heaters.=--It is sometimes more convenient to use the furnace as a means of heating water than the kitchen range. Such an arrangement is shown in Fig. 120, where a loop of pipe in the fire-box of the furnace takes the place of the water-back. The arrangement of the pipes in the range boiler are as before, the water entering the tank through the pipe _A_, circulates through the pipes _B_ and _C_, receiving its heat while passing through the loop in the furnace, in exactly the same way as in the water-back. It would be quite possible to also connect the kitchen range with the tank as shown by the dotted lines indicating the water-back. Such an arrangement would virtually be that shown in Fig. 116, where the two heaters on different floors are connected with the boiler.