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10
Installing the water heater.
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.
Water Supply Connections
Refer to the illustration on page 11 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.
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 connection
nipples.