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14
Temperature and Pressure
Relief Valve
For protection against excessive pressures and
temperatures, a temperature and pressure relief valve must
be installed in the opening marked “T & P RELIEF VALVE”
(see Figure 15). This valve must be design certified by
a nationally recognized testing laboratory that maintains
periodic inspection of the production of listed equipment or
materials as meeting the requirements for Relief Valves and
Automatic Shut-off Devices for Hot Water Supply Systems,
ANSI Z21.22. The function of the temperature and pressure
relief valve is to discharge water in large quantities in the
event of excessive temperature or pressure developing
in the water heater. The valve’s relief pressure must not
exceed the working pressure of the water heater as stated
on the data plate.
IMPORTANT: Only a new temperature and pressure relief
valve should be used with your water heater. Do not use an
old or existing valve as it may be damaged or not adequate
for the working pressure of the new water heater. Do not
place any valve between the relief valve and the tank.
The Temperature & Pressure Relief Valve:
• Must not be in contact with any electrical part.
• Must be connected to an adequate discharge line.
• Must not be rated higher than the working pressure
shown on the data plate of the water heater.
The Discharge Line:
• Must not be smaller than the pipe size of the relief
valve or have any reducing coupling installed in the
discharge line.
• Must not be capped, blocked, plugged or contain any
valve between the relief valve and the end of the dis-
charge line.
• Must terminate a maximum of six inches above a floor
drain or external to the building. In cold climates, it is
recommended that the discharge pipe be terminated at
an adequate drain inside the building.
• Must be capable of withstanding 250°F (121°C) without
distortion.
• Must be installed to allow complete drainage of both
the valve and discharge line.
Special Applications
Combination Space Heating/Potable
Water System
Some water heater models are equipped with inlet/outlet
tappings suitable for combination water (potable) heating
and space heating and not suitable for space heating
applications only. If this water heater is to be used to supply
both space heating and domestic potable (drinking) water,
the instructions listed below must be followed.
• Be sure to follow the manual(s) shipped with the air
handler system.
• This water heater is not to be used as a replacement
for an existing boiler installation.
• Do not use with piping that has been treated with
chromates, boiler seal or other chemicals and do not
add any chemicals to the water heater piping.
• If the space heating system requires water tempera-
tures in excess of 120°F, a mixing valve or an anti-
scald device should be installed per its manufacturer’s
instructions in the domestic (potable) hot water sup-
ply to limit the risk of scald injury. Also, install mixing
valves at each point of use.
• Pumps, valves, piping and fittings must be compatible
with potable water.
• A properly installed flow control valve is required to pre-
vent thermosiphoning. Thermosiphoning is the result
of a continuous flow of water through the air handler
circuit during the off cycle. Weeping (blow off) of the
temperature and pressure relief valve (T & P) or higher
than normal water temperatures are the first signs of
thermosiphoning.
• The domestic hot water line from the water heater
Figure 15
Temperature and Pressure
Relief Valve Installation
Discharge Pipe
(Do not cap or plug.)
6" Maximum
Air Gap
Metal Drain Pan
Temperature and
Pressure Relief Valve
Optional location
some models only
Floor
Drain
Drain Line
3/4” ID minimum
Explosion Hazard
If the temperature and pressure relief valve
is dripping or leaking, have a qualified
person replace it.
Examples of a qualified person include:
licensed plumbers, authorized gas company
personnel, and authorized service
personnel.
Do not plug valve.
Do not remove valve.
Failure to follow these instructions can
result in death, or explosion.
WARNING
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