Gas Piping; Gas Supply Systems; Gas Pressure Requirements; Supply Gas Regulator - A.O. Smith BTX 100 Instruction Manual

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).

Gas supplY sYsteMs

Low pressure building gas supply systems are defined as those
systems that cannot under any circumstances exceed 14"
W.C. (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).
gas supply pressure must be stable within 1.5" W.C. from static to
dynamic pressure to provide good performance. Pressure drops
that exceed 1.5" W.C. 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
appliance 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. (1/2 PSI Gauge). These systems must use field supplied
regulators to lower the gas pressure to less than 14" W.C. (1/2 PSI
Gauge). Appliances 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
often require multiple regulators to achieve desired pressures.
Systems in excess of 5 PSI building pressure should be designed
by gas delivery professionals for best performance. Water heaters
connected to gas supply systems that exceed 14" W.C. (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 3.5"
W.C.(0.87 kPa) for natural gas and 8.0 W.C. (1.99 kPa) for
propane. The minimum supply pressure is measured while gas
is not flowing (static pressure) AND while gas is flowing (dynamic
pressure). The supply pressure (static and dynamic) should never
fall below 3.5" W.C.(0.87 kPa) for natural gas or 8.0" W.C. (1.99
kPa) for propane. 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 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) AND while gas is flowing (dynamic pressure).

supplY Gas reGulator

The maximum allowable gas supply pressure for this water heater
is 14 inches W.C. (3.5 kPa). Install a positive lock-up gas pressure
regulator in the gas supply line if inlet gas pressure can exceed 14
inches W.C. (3.5 kPa) at any time. Regulators must be sized/used
according to manufacturer's specifications.
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. 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) from the water heater's inlet gas connection.
3. After installing the positive lock-up gas pressure regulator(s) an
initial nominal supply pressure setting of 7.0" W.C. while the water
heater is operating is recommended and will generally provide
good water heater operation. Some additional adjustment may
be required later to maintain a steady gas supply pressure.
4. 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.
All gas piping must comply with local codes and ordinances or with
the current editions National Fuel Gas Code (ANSI Z223.1/ NFPA-
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