Fuel Gas Piping and Gas Appliances
Sizing and materials
Gas piping is sized by the longest-length method: measure from the meter to the farthest appliance (developed length, including fittings), total the connected load in Btu/h, then read the table for the available pressure and allowable drop. Tables assume a gas specific gravity near 0.60 and a defined pressure drop - using a different gas or pressure invalidates the table. Approved materials include black steel, copper where permitted, and listed corrugated stainless steel tubing (CSST), which must be bonded to the grounding electrode system per its listing.
Installation rules that get tested
- Sediment trap (drip leg) downstream of the appliance shutoff and ahead of the controls.
- Shutoff valve in the same room and within the required distance of the appliance.
- Union or appliance connector for removal; connectors are limited in length (commonly 3 ft, longer for specific ranges) and cannot pass through walls, floors, or ceilings.
- Protection where piping passes through masonry or is concealed; no gas piping in chimneys, ducts, or elevator shafts.
- Leak testing with air or inert gas at the code-specified pressure and duration; never test with flame or oxygen.
Appliance side
Combustion air, venting/draft, clearances to combustibles, and correct category of vent material. Appliances in bedrooms, closets, or garages carry extra restrictions.
Worked example
A 40 ft run to a furnace with 60,000 Btu/h input: measure developed length with fittings, confirm the pressure available at the meter (often 7 in w.c. for natural gas), then select pipe size from the table for the total load on that segment - not just the farthest appliance.
Traps
Omitting the sediment trap; sizing only the last segment; skipping CSST bonding; and using a connector through a wall.