Installing the water heater.
6
Thermal Expansion
Typical Installation
Determine if a check valve exists in the inlet water line. Check with your local water
utility.
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.
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.
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.
R
E
L
I
E
F
V
A
L
V
E
COL
D
HO
T
Heat trap
6" minimum
Heat trap
6" minimum
6" air gap
Union
To electrical
distribution panel
Temperature
&
Pressure
Relief Valve
Anode
Union
Hot water outlet
to fixtures
Jacket access
panels
Drain valve
Auxiliary catch pan
2" maximum
Relief valve discharge line
to suitable open drain
Thermal
expansion tank
(if required)
Electrical junction box
(use only copper conductors)
To cold water
supply
Shut-off
valve
Vacuum Relief Valve
(Not Supplied)
If required, install per local codes
and valve manufacturer’s
instructions.
