Rheem AP15121-1 - Manual (Page 6)

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 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.
Water Supply Connections
Refer to the illustration on the next page
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. 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 traps.
Condensate Drains for the Heat Pump
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.
• Do not reduce drain line size less than
connection size provided on condensate
drain.
• All drain lines must be pitched
downward away from the unit a
minimum of 1/8" per foot of line to
ensure proper drainage.
• Do not connect condensate drain line
to a closed or open sewer pipe. 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.
• This unit is equipped with a 3/4"
primary condensate connection and a
1/2" overflow connection.