Pima County Development Services
Building Safety & Sustainability Division

Gas Distribution Standards

These standards are taken from Chapter 12 of the Uniform Plumbing Code to help the homeowner to replace, modify or reconnect a gas distribution system: For specific information refer to the Plumbing Code or contact the Building Codes Division of Pima County Development Services at 740-6490.

SIZING THE SYSTEM

• Gas systems are sized to ensure adequate gas pressure and volume is provided at each appliance outlet. To determine the size (diameter) of each section of pipe two things must be determined. The demand in BTU'S, for each gas appliance, and the length (developed length) of the piping from the gas meter to the appliance. See Table 12-1 for the demands of typical gas appliances. All appliances may be sized according to the listing plate attached to the unit.
• When the demands and developed lengths have been determined Table 12-3 is used for Sizing Natural Gas systems. Liquefied Petroleum (LP) systems use Table 12-7. There are several ways to use the tables. One method provides that each branch length may be sized according to the demand on that particular branch. Then, as each branch line joins the main trunk, the demands are added until the meter is reached. Another simple method uses the total developed length to size each branch (this method is presented with the table 12-3 for easy use).
• Other systems such as CSST are sized in accordance with the manufacturers instructions that are based on ANSI standards.

TABLE 12-1
Minimum Demand of a Typical Gas Appliances (if no nameplate indicating demand)

Appliance	BTU
Domestic gas range	65,000
Barbecue	50,000
Water Heater 40 gal.	50,000
Domestic top burners	40,000
Domestic dryer	35,000
Water Heater 30 gal.	30,000
Fireplace log lighter	25,000
Domestic oven	25,000

All other demands such as furnaces, boilers, etc., are dependent upon the demand listed on the appliance. To determine demand by cubic foot per hour (CFH) simply divide the BTU by 1,000. As an example, a 85,000 BTU furnace requires 85 CFH.

INSTALLATION

• Metal gas piping shall not be bent. Changes in direction shall be made by the use of fittings or combination of fittings. Non-metallic pipe may bend to a radius not less than 20 times the diameter of the pipe. 

The depth the pipe must be buried is:

Metal pipe.........12 inches minimum
Plastic pipe........18 inches minimum

An 18 ga. copper tracer wire must be installed with plastic pipe and must terminate above grade at both ends. Plastic pipe must be factory labeled with the words "natural gas”.

Good practice would support the pipe near joints to reduce strain at the fitting.

Piping above grade must be supported as follows:

• ½” Every 6 feet
• ¾” Every 8 feet
• 1¼”+ Every 10 feet

 

• Gas piping installed on a roof shall be supported 1 1/2 inches above the roof on blocks or approved supports on intervals indicated above.  
• Gas piping installed underground shall be factory wrapped (green coating). All joints shall be cleaned, coated with primer and wrapped with two layers of approved plastic tape. Standard IS 13-91 describes these requirements.
• All exposed piping shall be six inches above grade and properly supported.
• Unions shall not be buried or concealed. An accessible shut off valve shall be installed within three feet of each appliance in the same space with the appliance.

INSPECTIONS

• All excavations shall be left open until the piping has been tested, inspected and approved.
• All gas piping must be tested to verify there are no leaks. The test must maintain 10-psi minimum air pressure for at least 15 minutes with no loss of pressure. The installer is responsible to perform the test and supply the testing equipment. The test must remain in place for the inspector to observe.
• The inspection of chimneys and vents on gas appliances shall be made after they are installed and before they are covered or concealed.
• Combustion air must be provided for gas burning, appliances. Water heaters must be provided a F/T relief valve piped to the outside or an approved location.
• Reconnections require that the gas system be tested with a 10-psi air test as described in #2 above. Reconnection tests are required when the gas system has not been used for two months for industrial or commercial buildings, and 12 months for residential buildings.

TABLE 12-7 LP Gas

Liquefied Petroleum Gas piping systems are sized in the same manner as natural gas. LP gas has more BTU,s per cubic foot than natural gas so generally the piping will be smaller than natural gas piping. The table below has the developed length along the top and the pipe sizes on the left. The BTU outputs are arranged according to the length and pipe site the same as table 12-3. Use the procedure as described for natural gas but realize the columns are different.

Maximum Capacity of Pipe In Thousands of BTU per Hour of Undiluted Liquefied Petroleum Gases 
(Based on a Pressure Drop of 0.5 Inch Water Column)

  Low Pressure 11” Water Column