Installing the water heater.
Thermal Expansion
Water Supply Connections
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 softener.
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 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 the water heater and the
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 additional information
regarding this subject.
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
Refer to the illustrations on the following
page for suggested typical installation. 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. Connect cold water supply line to
3/4” pipe connection near bottom of water
heater on the 6 gallon and 20 gallon models.
Install a shut-off valve and a drain valve
(not supplied with heater, except 2 1/2 gal.
models) in cold water line near water heater.
Connect hot water line to 3/4” pipe
connection marked HOT on side near top of
water heater. On the 2 1/2 gallon models,
the hot and cold water connections are 1/2”
pipe connections and are located on top of
the heater. Local codes may require an anti-
siphon device on the water inlet of a side
connect water heater.
