Rheem RTGH-C95XLP Use And Care Manual page 51

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 and the resulting
pressure increase 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
Water Supply Connections
CAUTION:
IMPORTANT—DO NOT apply heat to the HOT or COLD water
connections. If sweat connections are used, sweat tubing
to the adapter before fitting the adapter to the water
connections on the water heater. Any heat applied to the
water supply fittings will permanently damage the internal
components of the water heater.
NOTICE:
In cold environments, ice can accumulate in the water
heater's connectors. Plug in the water heater power
cord for approximately 10 minutes before making these
connections. This will melt any ice buildup.
Plumbing should be carried out by a qualified plumbing
contractor in accordance with local codes.
Only use approved plumbing materials.
To allow the full flow capacity, it is recommended to
keep water inlet and outlet pipes 3/4" (1.9 cm) diameter
or larger.
To conserve energy and to prevent freezing, insulate
both COLD and HOT water supply lines. DO NOT
insulate the drain line or pressure-relief valve.
Recirculation
Direct recirculation is allowed, provided the loop is
thermostatically controlled, and a timer is used to turn
the pump off during off peak periods. The pump must
be sized for a minimum of 5 pgm at 25 ft of head plus
building head. A 10°F difference between the loop
thermostat setting and water heater temperature setting
must be maintained.
INSTALLATION INSTRUCTIONS
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 possibility the
heater itself.
NOTICE:
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.
The expansion tank is designed with a built-in air
cushion that compresses as the system pressure
increases. This relieves the over-pressure condition and
eliminates the repeat operation of the relief valve. For
other approved methods of thermal expansion, contact
an installing contractor, water supplier, or plumbing
inspector.
To ensure proper operation of the water heater, follow
these water pressure guidelines.
Operation of the water heater requires a minimum
water pressure of 14 psi (97 kPa) and a minimum water
flow rate of 0.4 gpm (1.5 lpm).
Water pressure of 40 psi (276 kPa) is required to
achieve maximum flow rate.
To maintain proper performance, there must be
sufficient water supply pressure.Required Water
Pressure =
Min. Operating Water Pressure (14 psi [97 kPa])
+ Pipe Pressure Loss
+ Faucet Pressure Loss
+ Safety Margin (more than 5 psi [34 kPa]).
To supply HOT water to upper floors, additional water
pressure will be required (0.44 psi [3 kPa] per foot of
height). Calculate the distance between the water inlet
of the water heater (ground level) to the HOT water
faucet farthest away from the water heater (upper floor
level).
Well water systems should be set to ensure a minimum
system pressure of 40 psi (276 kPa). The pressure
should remain constant and stable during the operation
of the water heater.
Gravity water pressure is not recommended. When
the water is supplied from a water supply tank, the
height of the tank, the diameter of the supply pipes, and
their relation to water pressure need to be taken into
consideration.
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