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Home / Code Guides / Gas Pipe Sizing

Natural Gas Pipe Sizing — BTU Demand, Longest Run & the Tables

Gas pipe sizing is a lookup, not a guess: add up the appliance BTU inputs, measure the longest run, and read the pipe size from the table for your material and pressure. The mistakes happen in the adding and the measuring.

RequirementModel Code StandardSection
DemandPiping is sized for the total input BTU/h of all connected appliances, taken from nameplates — not an assumed diversityIRC G2413.2
Longest-length methodThe default method sizes every segment using the table row for the distance from the meter to the farthest applianceIRC G2413.4.1
Sizing tablesCapacity tables by material (Schedule 40 steel, CSST, copper, PE) at the system pressure and a standard 0.5 in. w.c. pressure dropIRC Table G2413.4(1) et seq.
CSST bondingCorrugated stainless steel tubing systems must be direct-bonded to the grounding electrode system per the manufacturer and the codeIRC G2411.2
Shutoff valvesEach appliance needs an accessible shutoff in the same room within 6 ft of the applianceIRC G2420.5
Sediment trapsA sediment trap downstream of the shutoff at appliances other than ranges, dryers, outdoor grills and decorative appliancesIRC G2419.4

Worth knowing

  • Adding one big appliance — a tankless water heater at 150–199k BTU is the classic — can undersize the whole existing system, not just the new branch. Re-run the table for every segment.
  • A 3/4 in. steel line that fed a 40k BTU furnace fine will starve a 199k tankless at any real length: this is the most common “no hot water in winter” service call.
  • Two-psi systems with pounds-to-inches regulators use different table rows and can move far more gas in the same pipe — common in newer tract housing.
  • State amendments matter here (several states modify CSST and bonding rules) — and utilities have their own meter-sizing requirements on top of the code.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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