il instantaneous heaters are connected
with the piping direct.

Combinations of the above systems are in use and serve the purpose
for which they are intended. For instance, the tank can be
connected with a coal range and a gas coil heater, heat being
furnished by the range alone or the coil heater alone, or both can
be used at the same time. This combination can be connected with
the furnace in the cellar, and during the winter months, when the
furnace is in use, the water can be heated by the furnace coil. In
warm weather, when the furnace is out, the range can supply the
necessary heat. In hot weather the coil gas heater can supply the
heat.

CONNECTIONS OF TANK AND HEATING APPARATUS.--The ordinary house
boiler or hot-water storage tank has four connections, two on top,
one on the side, and one on the bottom. The top connections are
used for the entrance of cold water into the tank and for the
supply of hot water to the fixtures (see Fig. 71). The cold-water
inlet has a tube extending into the tank below the side connection.
This tube has a small hole filed in it about 6 inches from the top.
This hole is to break any syphonic action that may occur at any
time. The side connection is for the connection of the pipe coming
from the top of the water back. The bottom opening in the tank is
for the connection of the pipe coming from the lower water back
connection, also for draining the boiler. The circulation of the
water can be followed thus: cold water enters the boiler in the
tube and discharges into the boiler below the side connection. From
here it flows out of the bottom connection into the water back,
through the upper connection into the boiler, through the side
opening, then to the top of the boiler and out to the fixtures
through the fixture supply opening.

[Illustration: FIG. 71.--Storage tank, and coil heater with
thermostatic control valve.]

Fig. 69 shows a thermostatic control valve attached to the bottom
of a heater coil, and at the side of storage tank. The best
arrangement is at the bottom, for it does not shut off the gas
supply until the boiler is full of hot water.

CONNECTING TANK AND COIL GAS HEATER.--The boiler and the coil gas
heater have a different connection. The bottom of the tank and the
bottom of the heater are connected. The top of the heater and the
top of the boiler are connected. The accompanying sketch shows how
this connection is made. If the tee on the top of the boiler into