Fuel Gas Piping and Special Plumbing Systems
Fuel gas piping
Gas sizing converts appliance input to cubic feet per hour (natural gas is about 1,000 Btu per cubic foot at 0.60 specific gravity) and reads the gas table for the pipe length and allowable pressure drop (typically 0.5 in. w.c. for low-pressure systems). Length is measured along the longest run from the meter, with an allowance for fittings. Each appliance needs a shutoff valve, a sediment trap (drip leg), and a union or ground-joint fitting. Pipe must be protected through walls and against corrosion; CSST and metallic gas piping must be bonded to the grounding electrode system. Appliance connectors are limited (about 6 ft) and may not be concealed. Systems are pressure-tested before the meter is set.
Venting and combustion air
Appliance vent connectors slope up toward the chimney with clearance to combustibles, and combustion air openings are sized from Btu/h input, with one opening near the top and one near the bottom of the enclosure.
Special plumbing systems
Nonpotable water (gray water, rainwater, reclaimed) must be identified, marked, kept separate from potable piping, and cross-connection protected. Irrigation systems require backflow protection. Solar thermal systems need T&P protection and expansion control.
Traps in questions
- Sizing on total connected load instead of the longest run.
- Placing a shutoff or sediment trap on the wrong side of a regulator.
- Assuming gas piping needs no electrical bonding.
Worked example
A 40,000 Btu/h range needs 40 CFH. On a 60 ft run of 1/2 in. schedule 40 at 0.5 in. w.c. drop the table allows roughly 50 CFH, so 1/2 in. is adequate.