Installation Requirements; Gas Supply System; Gas Pressure Requirements; Supply Gas Regulator - A.O. Smith BTN-120 Instruction Manual

gas supply system

low pressure building gas supply systems are defined as those
systems that cannot under any circumstances exceed 14" W.C.
(3.48 kPa) (1/2 PSI Gauge). These systems do not require pressure
regulation. Measurements should be taken to insure that gas
pressures are stable and fall within the requirements stated on the
water heater rating plate. readings should be taken with all gas burning
equipment off (static pressure) and with all gas burning equipment
running at maximum rate (dynamic pressure). The gas supply pressure
must be stable within 1.5" W.C. (0.37 kPa) from static to dynamic
pressure to provide good performance. Pressure drops that exceed
1.5" W.C. (0.37 kPa) may cause rough starting, noisy combustion or
nuisance outages. Increases or spikes in static pressure during off
cycles may cause failure to ignite or in severe cases damage to water
heater gas valves. If your low pressure system does NOT meet these
requirements, the installer is responsible for the corrections.
High Pressure building supply systems use pressures that exceed
14" W.C. (3.48 kPa) (1/2 PSI Gauge). These systems must use field
supplied regulators to lower the gas pressure to less than 14" W.C.
(3.48 kPa) (1/2 PSI Gauge). Water heaters require gas regulators
that are properly sized for the water heater input and deliver the
rating plate specified pressures. Gas supply systems where pressure
exceeds 5 PSI (34.5 kPa) often require multiple regulators to achieve
desired pressures. Systems in excess of 5 PSI (34.5 kPa) building
pressure should be designed by gas delivery professionals for best
performance. Water heaters connected to gas supply systems that
exceed 14" W.C. (3.48 kPa) (1/2 PSI Gauge) at any time must be
equipped with a gas supply regulator.

gas pressure reQuirements

All models require a minimum gas supply pressure of 5.6" W.C.
(1.39 kPa). The minimum supply pressure is measured while gas
is flowing (dynamic pressure). The supply pressure (dynamic)
should never fall below 5.6" W.C. (1.39 kPa). The supply pressure
should be measured with all gas fired appliances connected to the
common main firing at full capacity. If the supply pressure drops
more than 1.5" W.C. (0.37 kPa) as gas begins to flow to the water
heater then the supply gas system including the gas line and/or
the gas regulator may be restricted or undersized. See Supply
Gas regulator section and Gas Piping section of this manual.
The low gas pressure switch will shut down the water heater if the
supply gas pressure drops below the minimum allowable value.
The gas valve on all models has a maximum gas supply pressure
limit of 14" W.C. (3.48 kPa). The maximum supply pressure is
measured while gas is not flowing (static pressure).

supply gas regulator

The maximum allowable gas supply pressure for this water
heater is 14.0 inches W.C. (3.48 kPa). Install a positive lock-up
gas pressure regulator in the gas supply line if inlet gas pressure
can exceed 14.0 inches W.C. (3.48 kPa) at any time.
If a positive lock-up regulator is required follow these instructions:
1. Positive lock-up gas pressure regulators must be rated at or
above the input Btu/hr rating of the water heater they supply.
2. Supply gas regulators shall have inlet and outlet connections
not less than the minimum supply gas line size for the water
heater they supply. See Table 8, page 23.
3. Positive lock-up gas pressure regulator(s) should be installed no
closer than 3 feet (1 meter) and no farther than 8 feet (2.4 meters)
of equivalent length from the water heater's inlet gas connection.
4. After installing the positive lock-up gas pressure regulator(s) an
initial nominal supply pressure setting of 7.0" W.C. (1.74 kPa) while
the water heater is operating is recommended and will generally
provide good water heater operation. Some addition adjustment
maybe required later to maintain a steady gas supply pressure.

installation reQuirements

5. When installing multiple water heaters in the same gas supply
system it is recommended that individual positive lock-up gas
pressure regulators be installed at each unit from the supply
gas connection on the water heater.

power supply

The water heaters covered in this manual require a 120 VAC,
1Ø (single phase), 60Hz, 15 amp power supply and must also
be electrically grounded in accordance with local codes or, in the
absence of local codes, with the National electrical Code, ANSI/
NFPA 70 or the Canadian electrical Code, CSA C22.1.

water temperature Control and mixing ValVes

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 6 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 10) 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.
taBle 6.
Water Temperature Time for 1st Degree Burn
°F (°C) (less Severe Burns)
110 (43) (normal shower temp.)
116 (47) (pain threshold)
116 (47) 35 minutes
122 (50)
131 (55) 5 seconds
140 (60) 2 seconds
149 (65)
154 (68) instantaneous
(U.S. Government Memorandum, C.P.S.C., Peter l. Armstrong, Sept. 15, 1978)
12
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.
Time for Permanent Burns
2nd & 3rd Degree
(Most Severe Burns)
45 minutes
1 minute 5 minutes
25 seconds
5 seconds
1 second 2 seconds
1 second