Chapter 5 of 612% of exam
Fuel Gas Piping
Fuel gas piping carries an invisible, explosive fuel through a building, so precision matters at every step. A C-36 plumber must size the pipe so each appliance receives enough gas at the right pressure, choose materials rated for the service, and install the safety fittings—shutoffs, sediment traps, regulators, and connectors—that keep the system controllable and clean. Finally, every gas system must be pressure-tested and proven leak-free before it is placed in service. This chapter walks through sizing, materials, fittings, testing, and the basics of appliance venting.
Sizing Gas Pipe by BTU and Length
Gas pipe is sized so that even at full demand the pressure drop from the meter to the farthest appliance stays within an acceptable limit. Two variables drive the size: the total gas load in BTUs per hour that a section must carry, and the developed length of pipe from the source to the appliance. Longer runs and larger loads require larger pipe. Installers use the code's sizing tables, entering with the longest length to the most remote outlet and the demand of each section, rather than sizing by guesswork.
Size for total connected load
Each section of piping must be sized to carry the combined BTU-per-hour demand of all appliances it serves at their rated input, not just the nearest appliance.
Use the longest developed length
Sizing tables are entered using the developed length from the meter or regulator to the most remote outlet, which sets the pressure-drop basis for the whole system.
Account for pressure and drop
The correct table depends on the system's operating pressure and the allowable pressure drop; a low-pressure two-pound-drop table differs from a standard half-inch water column drop table.
Convert fuel to BTU demand
Appliance input is expressed in BTU per hour; where only cubic feet per hour is known, it is converted using the heating value of the specific fuel gas being delivered.
Never undersize a branch
Each branch and appliance connection must independently satisfy the sizing tables so that a single small run does not starve an appliance and cause incomplete combustion.
Pipe and Tubing Materials
Several materials are approved for fuel gas, each with its own rules. Black (uncoated) steel pipe is the traditional workhorse; corrugated stainless steel tubing (CSST) is flexible and fast to route but requires bonding for lightning safety; and certain copper and semi-rigid tubing is allowed depending on the gas and local amendments. Material selection also depends on where the pipe runs—underground, exposed, or in contact with corrosive soils.
Steel pipe is widely accepted
Threaded black or galvanized steel pipe with approved fittings is a standard material for fuel gas distribution in and around buildings.
CSST must be bonded
Corrugated stainless steel tubing must be electrically bonded to the grounding electrode system per the manufacturer's listing to reduce the risk of arc-perforation from a nearby lightning strike.
Copper only where suitable
Copper or brass tubing may be used only where the gas being delivered does not contain enough hydrogen sulfide or other agents to corrode it, and where local rules permit.
Protect underground pipe
Metallic gas pipe installed underground must be protected against corrosion by approved coatings, wrapping, or cathodic means, and routed at an adequate depth.
Use listed fittings only
Joints and fittings must be approved for fuel gas service and compatible with the pipe material; ordinary plumbing solder joints are not acceptable for gas.
Shutoffs, Sediment Traps, Regulators, and Connectors
Control and cleanliness fittings make a gas system safe to operate and service. An accessible shutoff valve at each appliance lets a technician isolate it. A sediment trap—also called a drip leg—catches moisture and debris before they reach the appliance's gas valve. Regulators step the pressure down to what the appliance needs, and listed flexible connectors join the rigid piping to movable appliances.
Appliance shutoff within reach
An accessible manual shutoff valve must be installed within close reach of each gas appliance, ahead of the connector, so the appliance can be turned off for service or in an emergency.
Sediment trap before the control
A sediment trap (drip leg) is installed downstream of the appliance shutoff and as close as practical to the appliance inlet to capture moisture and particles before they reach the gas control valve.
Regulators where pressure exceeds rating
A listed pressure regulator must be provided where the supply pressure is higher than the appliance is rated to receive, and its vent must be handled per its listing.
Listed connectors, not concealed
Flexible appliance connectors must be listed, of adequate length, and not run through walls, floors, or partitions where they cannot be inspected.
One connector per appliance
A single appliance connector is used for one appliance and is not joined end to end with another connector to gain length.
Pressure Testing and Appliance Venting Basics
Before gas ever flows, the piping is pressurized with air or inert gas and watched to confirm it holds without loss, proving there are no leaks. After appliances are connected and lit, the installer confirms that combustion products vent properly so that carbon monoxide cannot accumulate. Venting basics—category, slope, termination, and clearances—round out a safe installation.
Pressure test before use
New or modified gas piping must be tested with air or an inert gas at a pressure and duration set by code and held without a measurable drop before the system is placed in service.
Isolate appliances during test
Appliances and regulators not rated for the test pressure are disconnected or valved off so the test does not damage them and the piping alone is proven.
Find leaks safely
Leaks are located with an approved gas detector or a non-corrosive bubble solution, never with an open flame.
Vent combustion products outdoors
Fuel-burning appliances must vent their combustion products to the outdoors through a vent or chimney suited to the appliance category and installed with the required slope and clearances.
Maintain vent termination clearances
Vent terminations must be located away from windows, doors, and air intakes by the required distances so exhaust cannot re-enter the building.
Test your knowledge
Practice questions on Fuel Gas Piping