Thermal Expansion; Water Supply Connections - Rheem 72V20-1 Use And Care Manual

Installing the water heater.
NOTICE: Do not apply heat to
the HOT or COLD water
connections. If sweat
connections are used, sweat
tubing to adapter before fitting
adapter to the water
connections on heater. Any
heat applied to the water
supply fittings will
permanently damage the dip
tube and/or heat traps.
6

Thermal Expansion

Determine if a check valve exists in the
inlet water line. It may have been
installed in the cold water line as a
separate back flow preventer, or it may be
part of a pressure reducing valve, water
meter or water softerner. A check valve
located in the cold water inlet line can
cause what is referred to as a "closed
water system". A cold water inlet line
with no check valve or back flow
prevention device is referred to as an
"open water system".
As water is heated, it expands in volume
and creates an increase in the pressure
within the water system. This action is
referred to as "thermal expansion".
In an "open water system", expanding
water which exceeds the capacity of the
water heater flows back into the city main
where the pressure is easily dissipated.
A "closed water system", however,
prevents the expanding water from flowing
back into the main supply line, and the
result of "thermal expansion" can create a
rapid and dangerous pressure increase in

Water Supply Connections

Refer to the illustrations on pages 8 and 9
for suggested typical installations. The
installation of unions or flexible copper
connectors is recommended on the hot and
cold water connections so that the water
heater may be easily disconnected for
servicing if necessary.
The HOT and COLD water connections
are clearly marked and are 3/4" NPT on
all models. Install a shut-off valve in the
cold water line near the water heater.
the water heater and system piping. This
rapid pressure increase can quickly reach
the safety setting of the relief valve,
causing it to operate during each heating
cycle. Thermal expansion, and the
resulting rapid and repeated expansion and
contraction of components in the water
heater and piping system can cause
premature failure of the relief valve, and
possibly the heater itself. Replacing the
relief valve will not correct the problem.
The suggested method of controlling
thermal expansion is to install an
expansion tank in the cold water line
between the water heater and the check
valve. The expansion tank is designed with
an air cushion built in that compresses as
the system pressure increases, thereby
relieving the over pressure condition and
eliminating the repeated operation of the
relief valve. Other methods of controlling
thermal expansion are also available.
Contact your installing contractor, water
supplier or plumbing inspector for addition
information regarding this subject.
SIDE CONNECT MODELS
CAUTION:
are equipped with a special Hot Outlet Tube
Assembly. Do not rotate the Hot Outlet Nipple
when making water connections. The nipple
MUST remain in a position with the indicating
mark facing up.