A.O. Smith BT-100-LP, Instruction Manual

Page: 13 / 47

13
Table 3
shows the approximate time-to-burn relationship
for normal adult skin. If anyone using hot water provided
by the water heater being installed fits into one of these
groups or if there is a local code or state law requiring a
certain water temperature at the point of use, then special
precautions must be taken.
In addition to using the lowest possible temperature
setting that satisfies demand of the application, a mixing
valve should be installed at the water heater or at hot
water taps to further reduce system water temperature.
See
Figure 11
(page 13) .
Mixing valves are available at plumbing supply stores.
Consult a Qualified Installer or Service Agency. Follow
mixing valve manufacturer’s instructions for installation of
the valves.
TABLE 3. APPROXIMATE TIME-TO-BURN
Water
Temperature °F
Time for
1st Degree Burn
(Less Severe Burns)
Time for Permanent Burns
2nd & 3rd Degree
(Most Severe Burns)
110 (normal shower temp.)
116 (pain threshold)
116 35 minutes 45 minutes
122 1 minute 5 minutes
131 5 seconds 25 seconds
140 2 seconds 5 seconds
149 1 second 2 seconds
154 instantaneous 1 second
(U.S. Government Memorandum, C.P.S.C., Peter L. Armstrong, Sept. 15,1978)
HOT WATER
OUTLET
TO TANK
INLET
CHECK
VALVE
MIXING
VALVE
COLD
WATER
INLET
TEMPERED WATER
OUTLET
12” TO 15”
(30-38 cm)
CHECK
VALVE
FIGURE 11. MIXING VALVE
WATER PIPING
WATER (POTABLE) HEATING AND SPACE HEATING
This water heater shall not be connected to any heating
systems or component(s) used with a non-potable water
heating appliance.
All piping components connected to this unit for space
heating applications shall be suitable for use with potable
water. Toxic chemicals, such as those used for boiler
treatment shall not be introduced into this system.
When the system requires water for space heating at
temperatures higher than required for domestic water
purposes, a mixing valve must be installed. See
Figure 11
(page 13) for suggested piping arrangement.
These water heaters cannot be used in space heating
applications only.
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 must be installed
on all closed systems to control the harmful effects of
thermal expansion. Contact a local plumbing service
technician to have a thermal expansion tank installed.