Fuel gas piping, venting, and combustion air
Fuel gas piping and venting
Fuel gas work requires load calculation, correct pipe sizing, and safe venting. Add the input Btu/h of all appliances, then size pipe by the longest equivalent length and available pressure using the adopted gas table. Include the meter, regulator, and fittings. Provide a shutoff valve and sediment trap at each appliance, and bond CSST as listed. Appliance connectors must be listed and not concealed. Combustion air must come from openings sized to the appliance input and the space; venting must match the appliance category and termination clearances.
Testing and safety
Gas piping is tested before concealment, usually with air or inert gas at the code-specified pressure. Leak-test gauges must be visible. Do not use gas for testing. Vent terminals must clear windows, doors, intakes, and property lines. A draft hood or induced-draft fan changes the venting requirements. Regulators need vent protection.
Worked example
A furnace draws 80,000 Btu/h, a water heater 40,000, and a range 65,000, totaling 185,000 Btu/h. The designer measures the longest run from the meter to the farthest appliance, including equivalent length for elbows and valves. Using the local gas table at the available pressure, the main is sized for 185,000 Btu/h and the longest length. The range branch is sized separately for 65,000 Btu/h. A smaller branch would starve the range during peak demand even if the main looks large.
Traps
Using output instead of input Btu/h; ignoring longest length; omitting sediment traps; improper CSST bonding; venting under an operable window; no combustion-air openings; testing with gas.