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Installing the water heater.
6
Thermal Expansion
Typical Installation
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 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 (refer to the 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.
R
E
L
I
E
F
V
A
L
V
E
COLD
H
OT
To electrical
distribution panel
Heat trap
6″ minimum
Heat trap
6″ minimum
To cold water
supply
Jacket access panel
Relief valve discharge line
to suitable open drain
Jacket access panel
Auxiliary catch pan
2″ maximum
Drain valve
Electrical junction box
(use only copper conductors)
Hot water outlet
to fixtures
6″ air gap
Anode
Shut-off valve
Union
Temperature and
pressure relief valve
Union
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.
Customer Service Troubleshooting Tips Care and Cleaning Operating Instructions Installation Instructions Safety Instructions
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″ NPT
on all models. Install a shut-off valve in the cold water line near the water heater.
Thermal
expansion tank
(if required)
Vacuum Relief Valve
(Not Supplied)
If required, install per local codes
and valve manufacturer’s
instructions.