red with rust when the water becomes hot enough to
circulate. When the pipes are stopped up, steam is formed and a
snapping and cracking sound is heard. To avoid these conditions,
the piping should be of brass or lead and the storage tank should
be of copper. The installation cost of brass and copper is greater
than steel, but they will not have to be replaced in two or three
years, as is the case with other material. A valve should be placed
on the cold-water supply to control the entire hot-water piping
system. A pipe with a stop cock should be placed underneath the
boiler and should extend into a sink in the basement so that the
boiler can be drained at any time for cleaning or repairs.

CONNECTING WITH FIXTURES.--To have all fixtures properly supplied
with hot water it is necessary to run what is termed a circulating
pipe. This circulating pipe is a circuit of pipe extending from the
top of the boiler to the vicinity of the fixtures and then
returning to the boiler and connecting into the pipe leading out of
the bottom of the boiler. From this circuit all branches are taken
to supply all fixtures requiring hot water. This circulating pipe
has hot water circulating through it all the time. Therefore the
fixtures are supplied with hot water very quickly. The circulating
pipe and its branches are run without any traps or air pockets.

[Illustration: FIG. 73.--Expansion loop. Four 90 deg. ells.]

[Illustration: FIG. 74.--Expansion loop. Five 90 deg. ells.]

[Illustration: FIG. 75.--Expansion loop. Six 90 deg. ells.]

When running the piping, it should be borne in mind that not only
does the water expand when heated, but the pipe expands also.
Therefore due allowance must be made for this expansion. The long
risers should have an expansion loop as shown in Figs. 73, 74 and
75. There are installed on some jobs what is known as an expansion
joint. This will allow for the expansion and contraction of the
pipe. The writer's experience with these joints has not been very
satisfactory. After a while these joints begin to leak and they
must have attention which in some cases is rather expensive. An
expansion loop as shown in the sketch, made with elbows, will prove
satisfactory. If the threads on the fittings and pipe are good, no
leak will appear on this joint.

All gas heaters must be connected with a flue to carry off the
products of combustion.

CHAPTER XV

INSULATION OF PIPING TO ELIMINATE CONDUCTION, RADI