Gas Piping System Notes

Gas Piping Systems

Sizing

  • Sizing is based on Chapter 4 of the 2015 International Fuel Gas Code.
  • Methods include Longest Length Method (402.4.1), Branch Length Method (402.4.2), and Hybrid pressure.
  • Maximum indoor pressure is 5 psi (402.6), with exceptions for:
    • Welded Fittings
    • Ventilated Chase
    • Industrial/Agricultural applications
    • Temporary construction
    • LP gas up to 20 psi
  • Common indoor gas piping systems:
    • 7” WC
    • 2 psi (requires gas utility permission)
    • 5 psi (requires gas utility permission)
  • Longest Length Method: All pipe sections are sized using the 80-foot column.

Pipe Materials (403…)

  • Acceptable Materials:
    • Wrought Iron
    • Steel (Black Steel)
    • Copper
    • Aluminum
    • Corrugated Stainless Steel Tubing (CSST)
    • Plastic (Polyethylene)
  • Unacceptable Materials:
    • Cast Iron – NO

Fittings (403.9…)

  • Steel:
    • Threaded joints with joint compound, Flanges, Welded
  • Copper:
    • Threaded joints with joint compound, Flanges, Welded, Press Fittings
  • Aluminum:
    • Brazed, Flared, Press Fittings
  • CSST:
    • Threaded connectors
  • Plastic (Polyethylene):
    • Heat Fusion

Installation (404…)

  • General:
    • Do not run gas piping through ducts, chimneys, elevator shafts, etc.
    • Concealed piping inside solid walls/partitions is prohibited unless in a chase or casing.
    • Concealed locations require threaded, brazed, welded, or listed fittings.
    • Underground piping requires a minimum 12” bury.
    • Underground piping to outside appliances requires an 8” bury if not susceptible to damage.
    • Do not run gas piping under a building; if necessary, use a sleeve open to the outdoors.
    • Underground penetrations of foundations are prohibited.
  • CSST:
    • Must be protected from damage (Shield Plates 404.7.3).
    • Must be bonded to the electrical grounding system.
  • Plastic Pipe (Polyethylene, PE) – 404.17:
    • Outdoors underground only.
    • Not within or under any building or slab.
    • Maximum 100 psi.
    • Must have a yellow 18ga tracer wire.
  • Sediment Trap (408.4):
    • Installed downstream of the appliance shutoff valve, close to the appliance inlet.
    • Use a tee fitting with a capped nipple in the bottommost opening.
    • Exceptions: Illuminating appliances, ranges, clothes dryers, decorative vented appliances, gas fireplaces, outdoor grills.
  • Gas Appliance Connection:
    • Maximum 6 ft connector in the same room.
  • Gas Train Components:
    • Dirt Leg, Regulator, Electric Gas Valve, Pipe Union, Manual Gas Valve, Low-pressure gas switch, High-pressure gas switch, PRV vent tubing
  • Medium Pressure Regulators (MP Regulators) – 410.1:
    • Must be accessible.
    • Protected from physical damage.
    • If indoors, must be vented outdoors OR equipped with a leak-limiting device.

Testing (406…)

  • Pressure:
    • 1-1/2 x the design pressure, or
    • Minimum 3 psi test
  • Test Medium:
    • Air, nitrogen, carbon dioxide, or inert gas (406.2).
  • Duration:
    • 1/2 hour per 500 cubic feet of pipe volume, or
    • 10 minutes minimum
  • Leakage:
    • Any pressure loss indicates a leak; correct and re-test.

Combustion Air and Exhaust Flues

  • Fuel-burning equipment needs supply air for combustion and ventilation.
  • Key for equipment operation and occupant safety (prevents oxygen depletion and gas buildup).
  • Supply air sources:
    • Outdoor Air
    • Indoor Air
    • Mechanical Supply
  • Combustion Air Methods:
    • Two Openings Method
      • Sized and located per Sections 304.6, 304.6.1
    • Single High Opening Method
      • Sized and located per Sections 304.6, 304.6.2
    • Indoor Air Standard Method
      • Sections 304.5, 304.5.1
      • Calculate required volume: 50 ft² per 1000 Btu
    • Combination Indoor/Outdoor Air
      • Determine indoor volume ratio and outdoor opening size per Section 304.7
    • Engineered System
      • Approval required per Section 304.8
    • Known Air Infiltration Rate Method
      • Sections 304.5, 304.5.2
      • Calculate required volume for fan-assisted appliances using Equation 3.2, otherwise Equation 3.1
    • Mechanical Supply
      • Air flow rate and system design per Sections 304.9 through 304.9.3
  • Indoor Air
    • 50 cubic feet per 1,000 Btu/h input needed.
    • High/low openings within 12 inches of ceiling/floor.
    • Opening area of 1 sq. in. per 1,000 Btu/h each.
  • Outdoor Air
    • High/low openings within 12 inches of ceiling/floor.
    • Opening area of 1 sq. in. per 2,000 Btu/h each if vertical.
    • Opening area of 1 sq. in. per 4,000 Btu/h each if horizontal.
  • Mechanical Supply
    • Direct-vent application
    • Combustion air duct size per manufacturer’s requirements, based on Btu/h input and length of duct.
    • Similar for exhaust flues.
    • Minimum separation distances and distances from grade outlined.