Gas Piping and Fuel Gas Systems
Fuel gas questions cover load calculation, pipe sizing, materials and leak testing. The CPC fuel gas chapter governs piping; the California Mechanical Code governs appliances and venting. Local amendments vary, so confirm the jurisdiction's adoption before you design.
Load and sizing
- Natural gas carries roughly 1,000 BTU per cubic foot, so appliance input divided by 1,000 gives cubic feet per hour.
- Typical inputs: range 65,000 BTU/h, dryer 35,000, water heater 40,000, furnace 80,000 to 100,000.
- Size from the longest run - meter to the farthest outlet including verticals - not from total pipe length. Use the low-pressure table for 0.5 inch water column drop at 0.60 specific gravity.
Materials and installation
Schedule 40 black steel and listed CSST are the standard choices; CSST must be bonded to the grounding electrode system and protected from puncture. Unions must remain accessible; no bushings; sleeves through masonry and concrete; sediment trap at every appliance; shutoff valve and a connector within the allowed length.
Testing
Piping is tested with air or nitrogen - never with gas, never with a flame. Low-pressure systems are commonly tested at 10 psi for 15 minutes, or at 1.5 times working pressure if higher; follow the CPC and the local requirement, and leave the gauge visible for the inspector.
Worked example
Load = water heater 40,000 + furnace 80,000 + range 65,000 + dryer 35,000 = 220,000 BTU/h = 220 CFH. Longest run is 25 ft from the meter to the manifold plus 45 ft to the furnace = 70 ft. At 70 ft, 3/4 inch steel carries roughly 130 to 140 CFH - too small. One inch steel carries roughly 250 CFH, so the main must be 1 inch, and only the short branch to the water heater may reduce.
Traps
- Sizing on total length instead of the longest run.
- Omitting the water heater or dryer from the load.
- Forgetting CSST bonding.
- Concealing a union, or running a connector through a wall.
- Pressure-testing with gas, or overpressurizing an air test.