of copper has become the most popular because
of coppers ability to resist corrosion that increases
in proportion to the temperature of the water.
Sizing of the piping for a hot-water system is done
the same way as for a cold-water system.
The layout of a hot-water system is designed
to carry heated water from a storage unit to
plumbing fixtures. Installation planning begins
with the water-heating device and a main supply
line from that device. The system should be
graded to a centrally located drip cock near the
water heater to allow for draining the system when
maintenance is required. Water for the individual
fixtures located throughout the facility is taken
off the main hot-water supply by risers as needed.
Each fixture riser should have a valve to make
repair work easier.
Buildings of considerable floor area or of
multifloor construction have the added problem
of supplying hot water to the fixture as soon as
possible after the tap is opened. In a one-pipe
system (such as that used for cold-water supply),
a lag occurs from the time the hot-water tap is
opened until the heated water travels from the the
water-heating device to the fixture. To overcome
this lag, a circulating water supply system is often
used. (See fig. 7-2.)
The circulating supply system is a two-pipe
system in which hot water flows from the heating
device through the main fixture risers and returns
to the heating device. This type of looped system
Figure 7-2.Hot-water circulating supply system.