This handout will guide you thru the basic, most common method for sizing a natural gas piping system for any residential or commercial application. There are other methods available for sizing these systems by either a complex formulaic method described in the California Plumbing Code, or the system can be engineered by a qualified professional. The information below is paraphrased from the California Plumbing Code and is provided as an aid to designers, contractors and homeowners who are installing or modifying a schedule 40 steel pipe, natural gas piping system.

Sizing of Gas Piping Systems.

Gas Piping systems shall be of such size and so installed as to provide a supply of gas to meet the maximum demand and supply gas to each appliance inlet at not less than the minimum supply pressure required by the appliance.

Maximum Gas Demand.

The volumetric flow rate of gas to be provided (in cubic feet per hour) shall be calculated using the manufacture’s input ratings of the appliance served, adjusted for altitude. Where the input rating is not indicated, the gas supplier, appliance manufacturer, or qualified agency shall be contacted or the rating from Table shall be used for estimating the volumetric flow rate of gas to be supplied. (Use 1,100)

The total connected hourly load shall be used as the basis for pipe sizing, assuming the appliances are operating in full capacity simultaneously.

Required Gas Supply.

Volume.

The hourly volume of gas required at each piping outlet shall be taken as not less than the maximum hourly rating as specified by the manufacturer of the appliance or appliances to be connected to each such outlet.

Where the rating of the gas appliance(s) to be installed is unknown, Table 1 shall be permitted to be used to estimate requirements of typical appliances. To obtain the cubic feet per hour of gas required, divide the input of the appliances by the average Btu (kW·h) heating value per cubic foot of the gas. The average Btu per cubic foot in the Bay Area is 1,100.

Minimum Size of Piping Outlets.

The size of the supply piping outlet for any gas appliance shall not be less than one-half (1/2) inch.

Pipe Sizing Methods.

Where the piping size is to be determined using either of the methods below, the minimum diameter of each pipe segment shall be obtained from the pipe sizing shown in Table 2.

Longest Length Method.

The size of each section of gas piping shall be determined using the total length of piping from the meter to the most remote outlet and the load of that section (see calculation example in “Figure A” use steps 1 – 5 below)

Branch Length Method.

Pipe shall be sized as follows: (See calculation example in “Figure A” and use steps 1 – 6 below)

  1. The pipe size of each section of the longest pipe run from the meter to the most remote outlet shall be determined using the longest run of piping and the load of the section.
  2. The pipe size of each section of branch piping not previously sized shall be determined using the length of piping from the meter to the most remote outlet in each branch and the load of the section.

Sizing of Piping Sections.

To determine the size of each section of pipe in any system use Table 2, and proceed as follows:

  1. Measure the length of the pipe from the gas meter location to the most remote outlet on the system.
  2. Locate that total length in the left-hand column of Table 2, or the next longer distance where the table does not give the exact length.
  3. Starting at the most remote outlet, find in the row just selected the gas demand for the outlet. Where the exact figure of demand is not shown, choose the next larger figure in the row.
  4. At the top of this column will be found the correct size of pipe.
  5. Using this same row, proceed in a similar manner for each section of pipe serving this outlet. For each section of pipe, determine the total gas demand supplied by that section.
  6. Size each section of branch piping not previously sized by measuring the distance from the gas meter location to the most remote outlet in that branch and follow the procedures of steps 2, 3, 4, and 5 above. Size branch piping in the order of their distance from the meter location, beginning with the most distant outlet not previously sized.