Fig. 79. Method of Connecting Reservoir to Two Water-Backs on Different Floors..

The means of heating may be a cast back or front, or a handmade pipe coil in the firebox. Air-traps favoring the formation of steam are occasioned by wrong inclination of the connection, by reduction of its diameter in the horizontal part, or by the upper hole of a cast back being tapped below the top of the water cavity. The bottom of a reservoir is below the firebox level when placed on the regular stand. When it is desirable to connect a reservoir with two water-backs, one in the kitchen range for regular service and another in a laundry stove in the cellar, the plan of connecting them seen in Fig. 79 is proper. In this case, either stove may be used separately, or both together, as occasion demands. The sediment cock of the upper reservoir may be handy to draw from at times; but the lower one will be found to collect most of the sediment, and should be opened frequently to cleanse the water-back and connections.

In laundries, public bathrooms, etc., where a large amount of hot water is used, it is necessary to have a larger storage tank and a heater with more heating surface than can be obtained in the ordinary range water-back. Fig. 80 shows an arrangement for this purpose, using the horizontal type of storage tank. The tank may be of galvanized wrought iron or steel, any size desired, and is usually suspended from the ceiling by means of heavy iron stirrups, pipe standards being placed from stirrups to floor for the larger sizes, while brick piers are best and usual for extra large tanks of 500 gallons or more. The heaters used are similar to those employed for hot-water house warming. The simplest method of making the connections is indicated in the illustration. If the supply is from a street service, or there are faucets on the storage tank below the hot storage reservoir level, allowing the tank to become empty through those faucets or failure of the street supply, there should be a check-valve in the cold-water connection.

The capacity of the heater and tank employed will depend upon the amount of water used. In some cases a large storage reservoir and a comparatively small heater are preferable, and in others the reverse is more desirable.

The required grate surface of the heater may be computed as follows: - First determine or assume the number of gallons to be heated per hour, and the required rise in temperature. Reduce gallons to pounds by multiplying by 8.3, and multiply the result by the required rise in temperature to obtain the number of thermal units. Assuming a combustion of five pounds of coal per square foot of grate, and an efficiency of 8,000 thermal units per pound of coal, we have the formula:

Grate surface in sq. ft. = Gal. per hour X 8.3 X Rise in temp.

5 x 8,000

Example. How many square feet of grate surface will be required to raise the temperature of 200 gallons of water per hour nected to Heater from 40 degrees to 180 degrees? Substituting values in the above formula, we have:

Fig. 80. Horizontal Type of Hot-Water Storage Cylinder Con.

200 X 8.3 X (180-40) / 5x8.000 = 5.8 square feet

In computing the amount of water required for bathtubs, it is customary to allow from 20 to 30 gallons per tub, and to consider that the tub may be used three or four times per hour as a maximum during the morning. This will vary a good deal, depending upon the character of the building. The above figures are based on apartment hotel practice.

Storage cylinders or reservoirs for hot water are often called boilers, but will henceforth be referred to as reservoirs. A stove or range connection is essentially described as follows: The sediment pipe should terminate in a faucet at the lowest point in the bottom connection, which connection should rise continuously from the lowest point to the bottom hole in the heater. No direct connection should ever be made between the water supply pipes and the drain. Even if such a connection is above the trap of a fixture, there is some danger that foul liquids or gases may penetrate for some distance into the supply pipes and thus afford a possibility of contamination of the water supply. The upper connection should rise continuously from the upper hole of the heater to the hole in the side of the reservoir; or, if preferred, in order to get hot water instantly after the fire begins, the upper connection may rise and connect into the main hot service over the reservoir. The circulation will be the same; but in general, connecting at the hole in the side gives best results, though in this case the first portion of water heated mingles with the balance in the upper end of the reservoir, and the following portions in succession, so that no hot water can be obtained until all the water above the side hole is warmed. The bottom hole serves for emptying, cleansing, and circulation to the stove.

The return circulation is always connected to the bottom pipe of the stove connection, as shown in Fig. 81, in which the hot service and circulating pipe are represented by dotted lines. The side hole is simply to receive the water from the stove. There are, or should be, two holes in the top, one in the center of the head, and the other about half the radius in the direction of the side hole. The concentric hole is for cold-water entry. The cold supply might be admitted at the bottom, but the result would be to empty the reservoir when the house supply is turned off. The cold supply is not emptied abruptly into the top of the reservoir. A delivery pipe is extended to very near the bottom, say within two or three inches, so that the water will mingle directly with the -coldest portion near the bottom, where it begins its journey to the stove to be heated. The usual way is by simple open-end pipe, but the end of the pipe should be plugged and holes drilled in the pipe and plug so as to form a spray delivery. This does not aid the delivery or heating at all, but the spray will scour the bottom and sides adjacent when the reservoir is emptied and flushed to rinse out scale and sediment. Immediately under the upper head, the delivery pipe must have a 1/8-inch hole drilled in, so that air will enter and break the siphon, and thus avoid inadvertently emptying the reservoir when intending only to cut off the supply and drain the pipe. See Fig. 78.