Instructions / Assembly

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
Heat trap
6” minimum
Heat trap
6” minimum
Union
To gas supply
Sediment trap
Cap
Ground joint 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
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.
Water Supply Connections
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 and
the heat traps in the hot/
cold nipples.
Shut-off valve
Shut-off
valve
Thermal expansion
tank (if required)
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.
Combustion Air
Inlet Openings
Hot water outlet to
fixtures
Water Heater Jacket
Vent connector to
chimney