Natural gas piping systems in multifamily buildings typically operate at standard delivery pressure. Standard delivery pressure at Southern California Gas Company is 8 inches water column (WC) or 1/3 pound per square inch gauge (PSIG). Southern California Gas Company’s 2 PSIG Program provides a higher than standard delivery pressure, 2 PSIG, to help reduce the size and cost of the gas piping system in new multifamily buildings.
Southern California Gas Company’s 2 PSIG program will help you cost effectively deliver the natural gas appliances and connections tenants prefer and builders know provide tenant comfort, retention and lower utility bills. Generally, multifamily units equipped with natural gas water heating, comfort heating, cooking and clothes drying have an operating cost much lower than electric alternatives. By delivering higher operating pressure, both the size and cost of the gas piping system can be reduced. Smaller pipe is easier to handle and install.
The 2 PSIG program is available for apartment, townhouse, and condominium projects in Southern California Gas Company service territory that meet all program requirements.
It is not the “pressure” that counts . . . it’s the “pressure drop” that moves the gas inside the pipe. Piping systems in apartments are traditionally operated at 8 in. water column (WC) or 1/3 PSI. By raising the pressure to 2PSI, several benefits become available when constructing multi-family units.
The pipe size is determined by the amount of energy that can be lost (also called the pressure drop) to move the gas, while leaving enough pressure to meet the minimum requirements of the appliance controls (usually 4 to 6 in. WC). As the pressure goes up, so too does the allowable pressure drop that can be accommodated. The greater the pressure drop, the greater the amount of gas that can be “pushed” through the pipe for a given size. For a given amount of gas, the pipe size can be decreased as the allowable pressure drop is increased. As shown in the figure below, the amount of gas (934 cubic feet per hour or CFH) that can be moved through a 100 ft long - 3/4 in. pipe (operated at 2PSI) would require a 2 in. diameter pipe when the same system is operated at 8 in. WC.
Simply put, 2PSI means lower costs. As multi-family buildings get larger and more complex with additional natural gas appliances, the traditional method of providing the required gas volume is accomplished by increased pipe size. The use of 2PSI will allow for reduced pipe sizing, resulting in material and labor cost savings and efficiencies.
A 2PSI system is actually two different systems combined into one. Although each system segment is designed separately, the overall objective is to minimize the pipe sizes and reduce the cost of the installation. The 2PSIG segment is used to bring the gas from the meter to each dwelling unit. In multi-family buildings, the distance from the meter to the first appliance is much greater than that commonly found in single family homes.
In many cases, this run of pipe can be 100 to 200 ft long. The use of 2PSI pressure will typically result in 1/2 or 3/4 inch pipe for this run compared to the 1 or 1-1/4 inch pipe commonly used in low pressure systems. Once inside the dwelling unit, a line regulator reduces the gas pressure to the traditional 8 in. WC. The line regulator is necessary because residential appliances are designed to burn gas only at low pressure.
There are many ways to configure the interior gas piping network, depending on the layout of the building and dwelling unit, the number of appliances per dwelling unit, and the location of the gas meters. The 2PSI program is based on Southern California Gas Company program requirements. Each multi-family building is somewhat unique when it comes to designing the meter bank needed to provide each apartment with its own gas meter.
The location of the building relative to the gas main in the street and the property line will influence the design of the meter bank. The location and design of the meter bank, in turn, will affect the design of the gas piping system inside the building. The following examples are but a few of the different possibilities. The piping system can incorporate any approved piping material and/or combination of materials.
Low rise installation with header and branch lines
Low rise installation with parallel branch lines
To eliminate any confusion, 2PSI gas piping systems can be sized using the traditional Longest Length Method in accordance with the UPC (Uniform Plumbing Code), but with a slight modification. The 2PSI system is broken down into two independent sections, and each section is sized separately.
From the meter to the line pressure regulator
Parallel branch line arrangement (2PSI section)
Header and branch line arrangement (2PSI section)
All piping downstream of the line pressure regulator
Parallel branch line arrangement (low pressure section)
Header and branch line arrangement (low pressure section)
Maximum deliver capacity of pipes of different diameters and lengths in cubic feet of gas per hour for an initial pressure of 2.0 PSI and a gas of .06 specific gravity.
Maximum deliver capacity of pipes of different diameters and lengths in cubic feet of gas per hour for an initial pressure of 7 inch water column with a 0.5 inch water column pressure drop and a gas of 0.6 specific gravity