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.
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” 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.
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.
Typical Installation
Heat trap
6” minimum
Heat trap
6” minimum
Union
To gas supply
Sediment trap
Cap
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
Ground joint union
Auxiliary catch pan
Union
Anode
Manual gas shut-off
Electronic control
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
Flammable vapor sensor