Closed System/Thermal Expansion; Temperature & Pressure Relief Valve - A.O. Smith HIGH EFFICIENCY ATMOSPHERIC VENTGAS WATER HEATER Use & Care Manual

Hot Water
Outlet
Metal Drain
Pan 1-3/4"
Depth Max.
Typical water piping installation
Unmixed
Hot Water
Hot Water
Outlet
Mixing Valve
(Set To 120 F)
Follow The Mixing Valve
Manufacturer's Instructions
Please note the following:
• The system should be installed only with piping that is
suitable for potable (drinkable) water such as copper,
CPVC, or polybutylene. This water heater must not be
installed using iron piping or PVC water piping.
• Use only pumps, valves, or fittings that are compatible
with potable water.
• It is recommend that only full flow ball or gate valves
are used in water piping installations. The use of valves
that may cause excessive restriction to water flow is not
recommended.
• Use only 95/5 tin-antimony or other equivalent solder.
Any lead based solder must not be used.
• Piping that has been treated with chromates, boiler seal,
or other chemicals must not be used.
• Chemicals that may contaminate the potable water
supply must not be added to the piping system.
In a closed system use a
thermal expansion tank
Cold Water
Pressure Reducing
Inlet Valve
Valve with Bypass
Cold Water Supply
to Fixture
Main Water
Supply
Temperature and Pressure (T&P)
Relief Valve (Optional Top T&P
Relief Valve Not Shown)
Massachusetts:
Install a vacuum relief
in cold water line per
section 19 MGL 142
Discharge line
(Do Not Cap or Plug)
1" Min.
Drain line 3/4"
ID Min.
6" Min.
Drain
FIGURE 13.
Mixed Water
To Fixtures
Cold Water
Inlet
0
FIGURE 14.

Closed System/Thermal Expansion

As water is heated, it expands (thermal expansion). In a closed
system, the volume of water will grow. As the volume of water
grows, there will be a corresponding increase in water pressure
due to thermal expansion. Thermal expansion can cause
premature tank failure (leakage). This type of failure is not
covered under the limited warranty. Thermal expansion can also
cause intermittent temperature-pressure relief valve operation:
water discharged from the valve due to excessive pressure build
up. The temperature-pressure relief valve is not intended for the
constant relief of thermal expansion. This condition is not covered
under the limited warranty.
A properly-sized thermal expansion tank should be installed
on all closed systems to control the harmful effects of thermal
expansion. Contact a plumbing service agency or your retail
supplier regarding the installation of a thermal expansion tank.
Temperature and Pressure Relief Valve
Metal Drain Pan
16
Explosion Hazard
• Temperature-pressure relief
valve must comply with ANSI
Z21.22-CSA 4.4 and ASME
code.
• Properly sized temperature-
pressure relief valve must be
installed in opening provided.
• Can result in overheating
and excessive tank pressure.
• Can cause serious injury or
death.
Temperature and
Pressure Relief Valve
(T&P)
Discharge line 3/4" Min.
Do not cap or plug.
6" Max.
Drain
FIGURE 15A.