Gas Piping - A.O. Smith BTR 120-400 Service Handbook

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 below. 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.- natural gas, (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.
*Screwed Fittings
It is important to guard against gas valve fouling from contaminants in 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. The instructions in this section on venting must
be followed to avoid choked combustion or recirculation of flue gases. Such conditions cause sooting or risks
of fire and asphyxiation.
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°Ell 0.7
90°Ell 1.6
Tee 3.1
Natural Gas 0.60 Specific Gravity, 0.50" W.C. Pressure Drop
Servicing should only be performed by a Qualified Service Technician
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
1 1/2"
200
200
200
200
200
200
200
200
200
1.9
4.0
8.0
7