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Gas piping symbols guide

Natural gas, propane, and specialty gas piping use a specific symbol vocabulary that overlaps with general plumbing but adds shutoffs, regulators, and meter conventions worth knowing.

Gas piping appears on plumbing or mechanical drawings, sometimes on its own dedicated sheet on larger commercial projects. The symbols follow general plumbing conventions but add gas-specific items: meters, regulators, drip legs, and emergency shutoffs. Each appliance has its own connection symbol and typically a CFH (cubic feet per hour) demand rating.

Pipe Line Symbols

G or NG
Natural gas (general). Letter callout on pipe line.
LPG / LP
Liquefied petroleum gas (propane).
MP, IP
Medium pressure or intermediate pressure gas (above 0.5 psi, typically up to 5 psi).
HP
High pressure gas (above 5 psi). Used to distribute over long distances; reduced at appliance.
O2, N2, N2O
Medical or industrial specialty gases. Use specific letter codes per NFPA 99 (medical) or facility standard.
U.G.
Underground portion of gas line. Typically shown dashed.

Service and Distribution Equipment

Meter (M)
Gas meter. Usually shown as a rectangle or circle with M inside. Utility-owned or building-owned depending on configuration.
Pressure Regulator
Reduces pressure from one stage to another. Shown as a triangle or hourglass symbol with inlet/outlet pressures called out.
Earthquake Valve
Automatic shutoff that closes during seismic events. Required by some jurisdictions in seismic zones.
Riser
Vertical pipe transition. Typically shown as a circle with up/down designation, often labeled with floor served.

Valves and Fittings

Gas Cock / Ball Valve
Quarter-turn shutoff. Required at every appliance and at the building entry. Often shown as a square or rectangle perpendicular to the line.
Sediment Trap (Drip Leg)
Tee with capped vertical extension below. Required ahead of each appliance per IFGC. Catches debris before it reaches the valve.
Union
Disconnectable joint. Required for appliance servicing. Two parallel lines with bolts.
Cap / Plug
Termination of a gas line. Used for future appliance stub-outs.

Appliance Connection Notation

Each gas appliance gets a connection symbol with the demand in CFH or BTU/hr. A range might be 60,000 BTU/hr; a furnace 100,000; a water heater 40,000. The drawings list each appliance and its load.

Pipe sizing depends on cumulative demand and pipe length. The longest run plus accumulated demand drives the upstream pipe size. Sizing tables in the IFGC (or NFPA 54) determine the diameter at each segment. The drawings should show pipe sizes called out at each branch and a sizing schedule for verification.

Special Notations and Codes

CSST
Corrugated stainless steel tubing. Listed as alternative to threaded steel piping. Specific bonding requirements per CSA LC-1.
Sch 40 Black
Schedule 40 black steel piping. Standard for indoor gas distribution.
PE
Polyethylene. Used for underground service connections to the meter.
SC / SS
Service connection / shutoff. Symbol and tag for the building's primary gas shutoff.

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Find gas piping errors across your drawings

Helonic checks gas piping symbols, sizing, and shutoff placement against IFGC requirements and architectural appliance schedules.