Use and Care Manual
9
Thermal Expansion
Determine if a check valve exists in the
inlet water line. Check with your local
water utility company. 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 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 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 (see
illustration below). 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.
Typical Installation
Water Supply Connections
Refer to the illustration below 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 if necessary. The HOT and COLD
water connections are clearly marked and are
3/4 in. NPT on all models. Install a shut-off
valve in the cold water line near the water
heater.
IMPORTANT: 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 cold water
connections on heater.
Any heat applied
to the cold water
supply fittings will
permanently damage
the dip tube.
NOTICE: The
National Fuel Gas
Code (NFGC)
mandates a manual
gas shut-off valve: See
(NFGC) for complete
instructions. Local
codes or plumbing
authority requirements
may vary from
the instructions or
diagrams provided and
take precedent over
these instructions.
Heat trap 6” minimum
Heat trap 6” minimum
Union
To gas supply
Sediment trap
Cap
Union
Drain Pan Pipe
to suitable drain.
Drain
valve
Relief valve discharge
line to suitable open
drain.
To cold water supply
6” Air gap
Draft hood
Pitch up 1/4” per foot
Auxiliary drain pan
Union
Anode
Manual gas shut-off
Thermostatic gas valve
Jacket door
Temperature and pressure
relief valve
Shut-off valve
Shut-off valve
Thermal expansion
tank (if required)
Combustion Air
Inlet Openings
Hot water outlet to
fixtures
Water Heater Jacket
Vent connector to
chimney