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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
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.
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
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
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
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