Thermal Expansion; Water Supply Connections; Condensate Drain - Rheem HB Duct Ready Series Use & Care Manual

Installing the water heater
6

Thermal Expansion

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 Supply Connections

Refer to the illustration on the next page
for suggested typical installation. The
installation of flexible connectors is
recommended on the hot and cold water
connections. Flexible connections provide
vibration isolation and allow the water heater
to be easily disconnected for servicing if
necessary. The HOT and COLD water
connections are clearly marked and are
3/4in. NPT on all models. Install a shut-off
valve in the cold water line near the water
heater.
Condensate Drains
Consult local codes or ordinances for
specific requirements. Refer to page 7.
IMPORTANT: When making drain fitting
connections to the drain tubing, use a thin
layer of piping tape or silicone and install
hand tight.
IMPORTANT: When making drain fitting
connections to the drain tubing, DO NOT
overtighten. Overtightening fittings can split
pipe connections on the drain pan.
• This unit is equipped with a 3/4" NPT
female primary condensate connection
and a 3/8" NPT female overflow
connection. Use MIP fittings for
connections.
• DO NOT reduce drain line size less
than connection size provided on

condensate drain.

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
on the next page). 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.
See page 8 on "To Fill The Water Heater".
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
• All drain lines must be pitched
downward away from the unit a
minimum of 1/8" per foot of line to
ensure proper drainage.
• Drain lines must include a P-trap if
connected to a sewer pipe.
• If no drain is available, then a common
condensate pump with a capacity no
less than 2 gallon per day must be
installed.
• DO NOT allow condensate to drain into
the water heater drain pan.
• The drain line should be insulated
where necessary to prevent sweating
and damage due to condensate forming
on the outside surface of the line.
traps.