In the supplying of hot water for large buildings the boiler is generally of the horizontal style, hung by wrought-iron hangers from the cellar timbers, although vertical boilers are sometimes used. The source of heat for such boilers is generally a special tank heater. Live and exhaust steam are also much used by means of steam coils placed inside the boiler. A combination often used to advantage includes both tank heater and steam coils, the heater being used during the summer and the coils during the winter season, when the heating plant of the building is in operation. The use of the tank heater and steam coil is seen in Fig. D, Plate 54.

In addition, special heating devices or auxiliaries are used in this work, one of them, known as the P. P. Heater, being shown connected to the boiler in Fig. E, and a sectional view of the same in Fig. F, Plate. 54. As seen from the latter, the device consists essentially of three pipes, one inside the other. Cold water is conducted through the innermost pipe, from which it passes into the pipe or tube next outside, this pipe being closed at its end.

Plate LIV. Hot-Water Supply For Large Buildings

Hot Water Supp/y Plate 54.

for Large Buildings

Hot Water Supply For Large Buildings 129Hot Water Supply For Large Buildings 130Hot Water Supply For Large Buildings 131

Fig.C.

Hot Water Supply For Large Buildings 132

Fig.D.

Hot Water Supply For Large Buildings 133Hot Water Supply For Large Buildings 134

Fig-F.

Steam is conveyed into the space between the middle pipe and the outer one, thus entirely surrounding the cold water that enters.

The flow connection is made to the middle pipe, also the draw-off connection. It is claimed that the heating of water by means of this heater is very rapid, and that even in the form of steam vapor it will heat the water more rapidly and in greater quantity than it can be heated by a water front with a hot fire.

The heater may be connected with the steam piping of the building, as shown in Fig. E.

The heater is made in several sizes, ranging from the kitchen-boiler size to sizes suitable for large work. The size of hot-water boilers naturally depends on the character and use of the building, the number of apartments, and number of fixtures supplied with hot water. In the case of apartment buildings it is generally a comparatively simple matter to approximate the boiler capacity necessary, but in the case of many buildings, experience and judgment are necessary in arriving at a proper size.

A very common method, and one that is ordinarily a safe one to follow, is to estimate about 20 gallons of boiler capacity for each full set of fixtures that would commonly require hot water in an apartment. These fixtures would include the kitchen sink, wash trays, bath tub, and lavatory. If any of these fixtures are omitted, or others are added, a due allowance may be made.

Reckoning on this basis, the following table shows the boiler capacity necessary for different numbers of apartments, and the standard sizes of boilers having the respective capacities.

Table Of Hot-Water Boiler Capacities

No. of Apartments

Capacity of Boiler

Size of Boiler

4........

. . . . 100 gals.

22" X 60"

6........

....120 "

24" X 60"

8........

....180 "

30" X 60"

10........

....215 "

30" x 72"

12........

....250 "

30" X 84"

16........

••..365 "

36" X 84"

20........

....430 "

42" x 72"

24........

...575 "

42" x 96"

36........

720 "

42" X 120"

Another table which will be found of value is the following, which shows the number and size of steam coils necessary for the several sizes of hot-water boilers specified in the foregoing table.

Table Of Steam Coils For Hot-Water Boilers

Capacity of Boiler

Size and Number of Coils

100 to 120 gals.....

180 "215 " .....

250 "365 " .....

430 " 575 " .....

720 " .....

....... 4 1-in. pipes.

....... 6 I-in.

....... 6 1 1/4-in. "

....... 4 1 1/2-in. "

....... 6 1 1/2-in. "

In Figs. A, B, and C, of Plate 54, are shown three different methods of installing large hot-water supply systems.

Of the three systems, probably that shown in Fig. A is least satisfactory, for the reason that the supply at different points is less evenly heated than in the case of the other two systems. For instance, the hot-water branches taken out of the return will not deliver such hot water as those on the flow line. However, the choice of a hot-water supply system must often depend upon the character and construction of the building to be supplied. All things being equal, the overhead system shown in Fig. C will probably do as satisfactory work as any of the others shown, although the system in Fig. B is an excellent one. The latter should be provided at its high point with an air vent, while the former needs none.