Mixing Valves; Gas Piping - A.O. Smith BTXL-100 Instruction Manual

MIXING VALVES

Water temperature over 125°F (52°C)
can cause severe burns instantly
resulting in severe injury or death.
Children, the elderly and the
physically or mentally disabled are at
highest risk for scald injury.
Feel water before bathing or
showering.
Temperature limiting devices such as
mixing valves must be installed
when required by codes and to
ensure safe temperatures at fixtures.
Water heated to a temperature which will satisfy clothes washing,
dish washing, and other sanitizing needs can scald and cause
permanent injury upon contact. Short repeated heating cycles
caused by small hot water uses can cause temperatures at the
point of use to exceed the water heater's temperature setting by
up to 20°F (11°C).
Some people are more likely to be permanently injured by hot water
than others. These include the elderly, children, the infirm and the
physically/mentally disabled. Table 4 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 the demand of the application a Mixing Valve should be
installed at the water heater (see "Figure: 9") or at the hot water
taps to further reduce system water temperature.
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.
In all cases, the following burn table must be used.
Water Temperature Time for 1st Degree Burn
°F (°C) (Less Severe Burns)
110 (43.3) (normal shower temp.)
116 (46.7) (pain threshold)
116 (46.7)
122 (50)
131 (55)
140 (60)
149 (65)
154 (67.8) instantaneous
(U.S. Government Memorandum, C.P.S.C., Peter L. Armstrong, Sept. 15, 1978)
Table 4
Time for Permanent
Burns
2nd & 3rd Degree
(Most Severe Burns)
35 minutes 45 minutes
1 minute 5 minutes
5 seconds 25 seconds
2 seconds 5 seconds
1 second 2 seconds
1 second

GAS PIPING

Make sure gas supplied is same type listed on model rating plate. The
inlet gas pressure must not exceed 14 inch water column (3.5 kPa) for
natural and propane gas (L.P.). The minimum inlet gas pressure shown
on rating plate is that which will permit firing at rated input.
SEDIMENT TRAPS
A sediment trap shall be installed as close to the gas inlet of the
water heater as practical at the time of water heater installation. The
sediment trap shall be either a tee fitting with a capped nipple in the
bottom outlet or other device recognized as an effective sediment
trap.
Contaminants in the gas lines may cause improper operation of the
gas control valve that may result in fire or explosion. Before attaching
the gas line be sure that all gas pipe is clean on the inside. To trap
any dirt or foreign material in the gas supply line, a sediment trap
must be incorporated in the piping. The sediment trap must be readily
accessible. Install in accordance with the Gas Piping section. Refer
to the current edition of the National Fuel Gas Code (ANSI Z223.1/
NFPA 54) or the Natural Gas and Propane Installation Code (CAN/
CSA B149.1)
Use pipe joint compound or teflon tape marked as being resistant to
the action of petroleum [Propane (L.P.)] gases.
The water heater and its gas connection must be leak tested before
placing the water heater in operation.
The water heater and its individual Shut-off valve shall be disconnected
from the gas supply piping system during any pressure testing of that
system at test pressures in excess of 1/2 pound per square inch (3.5
kPa). It shall be isolated from the gas supply piping system by closing
its individual manual Shut-off valve during any pressure testing of the
gas supply piping system at test pressures equal to or less than 1/2
pound per square inch (3.5 kPa).
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