Closed Water Systems; Thermal Expansion - A.O. Smith 100 Series Installation And Operating Manual

Table 17. Burn Time at Various Temperatures
Time for 1st
Water Temperature Degree Burns
°C (°F) (Less Severe Burns)
44 (110) (normal shower temp.)
47 (116) (pain threshold)
47 (116) 35 minutes
50 (122)
55 (131) 5 seconds
60 (140) 2 seconds
65 (149) 1 second
68 (154) instantaneous
(U.S. Government Memorandum, C.P.S.C., Peter L. Armstrong, Sept. 15,1978)
In addition to using lowest possible temperature setting that
satisfies demand of application, to reduce the risk of scalding, install
Thermostatic Mixing Valves (temperature limiting valves) at each
point-of-use. See Figure 34 (page 28).
These valves automatically mix hot and cold water to limit the
temperature at the tap.
Thermostatic Mixing Valves are available from your local plumbing
supplier. Consult a Qualified Installer or Service Agency. Follow
mixing valve manufacturer's instructions for installation of the
valves. Before changing the factory setting on the control system,
see Temperature Regulation (page 38).
WARNING
Toxic Chemical Hazard
• Do not connect to non-potable water system.

CLOSED WATER SYSTEMS

Water supply systems may, because of code requirements or such
conditions as high line pressure, among others, have installed
devices such as pressure reducing valves, check valves, and back
flow preventers. Devices such as these cause the water system to
be a closed system.

THERMAL EXPANSION

As water is heated, it expands (thermal expansion). In a closed
system the volume of water will grow when it is heated. 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. This condition is not covered under the limited warranty. The
temperature-pressure relief valve is not intended for the constant
relief of thermal expansion.
A properly sized thermal expansion tank should be installed on all
closed systems to control the harmful effects of thermal expansion.
Contact a local plumbing service agency to have a thermal expansion
tank installed.
Time for Permanent Burns
2nd & 3rd Degree (Most
Severe Burns)
45 minutes
1 minute 5 minutes
25 seconds
5 seconds
2 seconds
1 seconds
CAUTION
Property Damage Hazard
• Avoid water heater damage.
• Install thermal expansion tank if necessary.
• Do not apply heat to cold water inlet.
• Contact qualified installer or service agency.
Note: To protect against untimely corrosion of hot and cold water
fittings, it is strongly recommended that di-electric unions or
couplings be installed on this water heater (see Figure 36)
when connected to copper pipe. See Figure 36.
Figure 36. Using Di-Electric Unions or Couplings
Figure 36 also shows the typical attachment of the water piping to the
water heater. The water heater is equipped with 3/4" NPT connections
for all models.
Note: If using copper tubing, solder tubing to an adapter before
attaching the adapter to the water heater connections. Do not
solder the water lines directly to the water heater connections.
It will damage the tank, T&P Valve and Pipe Insulation (if
supplied).
Fit pipe insulation over the incoming cold water line and the hot
water line. Make sure that the insulation is against the top cover of
the heater. Fit T&P valve insulation over valve. Make sure that the
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