Gas Piping; Supply Gas Regulator; Gas Line Leak Testing; Purging - A.O. Smith BTR 151 Instruction Manual

gas piping

Contact your local gas service company to ensure that adequate
gas service is available and to review applicable installation
codes for your area.
Size the main gas line in accordance with Table 7. The figures
shown are for straight lengths of pipe at 0.5 in. W.C. pressure
drop, which is considered normal for low pressure systems.
note: Fittings such as elbows, tees and line regulators will add
to the pipe pressure drop. Also refer to the latest version of the
national Fuel gas Code.
Schedule 40 Steel or Wrought Iron Pipe is the preferred material
for the gas line of this water heater. It is imperative to follow the
sizing recommendations in the latest version of the national Fuel
Gas Code if Corrugated stainless steel Tubing (CssT) is used
as the gas line for this water heater.
The heater is not intended for operation at higher than 14.0" W.C.
(3.49 kPa) (1/2 pound per square inch gage) supply gas pressure.
Exposure to higher supply pressure may cause damage to the
gas valve which could result in fire or explosion. If overpressure
has occurred such as through improper testing of gas lines or
emergency malfunction of the supply system, the gas valve must
be checked for safe operation. Make sure that the outside vents
on the supply regulators and the safety vent valves are protected
against blockage. These are parts of the gas supply system, not
the heater. Vent blockage may occur during ice storms.
taBle 7. gas supply pipe lengths (in feet)
maximum equivalent pipe length - natural gas only
Schedule 40 Steel or Wrought Iron Pipe
Input Rate
(BTu/HR) 1/2"
120,000 20
154,000 10
180,000 -
199,000 -
250,000 -
275,000 -
310,000 -
366,000 -
390,000 -
Fitting Type*
45° EII 0.7
90° EII 1.6
Tee 3.1
natural gas 0.60 Specific gravity, 0.50" W.C. Pressure Drop
*Screwed Fittings
It is important to guard against gas valve fouling from contaminants
in the gas ways. Such fouling may cause improper operation, fire
or explosion.
If copper supply lines are used they must be internally tinned and
certified for gas service. 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, see Figure 20. The
sediment trap must be readily accessible and not subject to freezing
conditions. Install in accordance with recommendations of serving
gas suppliers. Refer to the current editions of the national Fuel
gas Code or B149.1 natural gas and Propane installation code.
To prevent damage, care must be taken not to apply too much
torque when attaching gas supply pipe to gas valve inlet.
Apply joint compounds (pipe dope) sparingly and only to the
male threads of pipe joints. Do not apply compounds to the first
3/4" 1" 1 1/4"
70 200 200
40 150 200
30 100 200
30 90 200
20 60 200
10 50 200
10 40 150
- 30 100
- 20 100
Equivalent length in Feet
1.0 1.2 1.6
2.1 2.6 3.5
4.1 5.2 6.9
two threads. use compounds resistant to the action of liquefied
petroleum gases.
gas meter siZe – natural gases only
Be sure the gas meter has sufficient capacity to supply the full
rated gas input of the water heater as well as the requirements of
all other gas fired equipment supplied by the meter. If gas meter
is too small, ask the gas company to install a larger meter having
adequate capacity.
gas piping and sediment trap installation

gas line leak testing

1 1/2"
200
200
200
200
200
200
200
200
200
1.9
Any time work is done on the gas supply system perform a leak
4.0
test to avoid the possibility of fire or explosion.
8.0
1. For test pressures exceeding 1/2 psi (3.45 kPa) disconnect
the water heater and its Main Gas shutoff Valve from the
gas supply piping system during testing, see Figure 20. The
gas supply line must be capped when disconnected from the
water heater.
2. For test pressures of 1/2 psi (3.45 kpa) or less, the appliance
need not be disconnected, but must be isolated from the supply
gas line by closing the Main gas Shutoff Valve during testing.
3. Coat all supply gas line joints and connections upstream of the
water heater with a non-corrosive soap and water solution to
test for leaks. Bubbles indicate a gas leak. Do not use matches,
candles, flame or other sources of ignition for this purpose.
4. Repair any leaks before placing the water heater in operation.

purging

gas line purging is required with new piping or systems in which
air has entered.
Purging should be performed per the current edition of nFPA
54, the national Fuel gas Code.
22
figure 20.
Fire and Explosion Hazard
Use joint compound or Teflon tape
compatible with propane gas.
Leak test before placing the wateheater
in operation.
Disconnect gas piping and main gas
shutoff valve before leak testing.
Install sediment trap in accordance
with NFPA 54.