7.4 Fuel Gas Basics, Combustion Air, Venting & Alabama Gas Fitting Scope

Why this section matters

The 2021 International Fuel Gas Code (IFGC) is one of the six approved references for the Journeyman Plumber exam. Plumbers install gas water heaters, and Alabama Plumbing and Gas Law questions test where plumbing ends and gas fitting begins.

The Alabama line between plumbing and gas fitting

• Gas fitting (§34-37-1(4)) means installing or repairing pipes, fixtures, appliances or apparatus that supply natural gas, from the point of delivery. It includes all gas piping before the combustion zone, the venting of flue gases and the air for combustion and ventilation.
• Plumbing and gas fitting are separate certifications (apprentice, journeyman and master in each).
• The Board's exam page says a person who passes a Journeyman or Master Plumber exam must hold at least an apprentice gas fitter certification to keep doing gas fitting. The reverse applies to gas fitters doing plumbing.
• Rule 720-X-3-.02: Gas piping up to and including the isolation (shutoff) valve is gas pipe fitting. Piping from the shutoff valve to a fixture or appliance is not gas fitting, except for gas-fired water heaters. For a gas water heater, the connection beyond the valve is also gas fitting.
• Rule 720-X-3-.01: Water heaters may be exchanged by a certified plumbing contractor or a certified gas fitting contractor.
• HVAC contractors certified by the Alabama HVACR Board may install and service gas-fired air heating and cooling appliances, but not the gas piping to them (§34-37-1(4)), and may install vents on gas heating equipment (r. 720-X-8-.01).
• Gas-related violations carry a minimum $1,000 fine under rule 720-X-4-.01(4), compared with $500 for other violations.

Fuel gas properties

Both gases are odorized so leaks can be smelled. Never use a flame to find a leak. Use an approved gas detector or noncorrosive leak-detection fluid (IFGC 406.5.1).

Combustion air (IFGC 304)

Indoor air, standard method (304.5.1): the space must have at least 50 cubic feet per 1,000 Btu/h of total appliance input. Example: a 40,000 Btu/h water heater plus an 80,000 Btu/h furnace equals 120,000 Btu/h, which needs $120 \times 50 = 6{,}000$ cubic feet. With an 8-foot ceiling, that is 750 square feet of floor. A smaller room needs combustion air openings.

• The minimum dimension of any opening is 3 inches.
• Louvers (304.10): use the actual free area if it is known. Otherwise assume wood 25% and metal 75%. Screens must have mesh no smaller than 1/4 inch. Motorized louvers must be proven open before the burner fires.

Example. A closet holds 120,000 Btu/h of appliances and gets outdoor air through two horizontal ducts. Each needs $120{,}000 \div 2{,}000 = 60$ square inches of free area. With metal louvers of unknown free area, each louver must be $60 \div 0.75 = 80$ square inches gross.

Appliance connections

• Appliance shutoff valve (IFGC 409.5.1): in the same room, within 6 feet of the appliance, upstream of the union or connector, and accessible. A valve behind a range or dryer counts as accessible. Valves for decorative appliances and room heaters may be remote under 409.5.2, and manifold valves may be up to 50 feet away under 409.5.3.
• Sediment trap (408.4): unless the appliance has one built in, install a tee with a capped nipple in the bottom outlet, downstream of the shutoff valve and as close to the appliance inlet as practical. It is not needed for illuminating appliances, ranges, clothes dryers, decorative vented appliances, gas fireplaces or outdoor grills.
• CSST bonding (IFGC 310.2): CSST without an arc-resistant jacket must be bonded to the electrical service grounding electrode system with a jumper at least 6 AWG copper, no more than 75 feet long, using listed (UL 467) clamps. Arc-resistant-jacketed CSST is considered bonded through the appliance's equipment grounding conductor (310.3).

Venting basics

• Category I appliances, such as atmospheric water heaters, vent by gravity through a Type B double-wall gas vent. Listed Type B vent typically needs 1 inch of clearance to combustibles.
• A single-wall metal connector from a draft-hood appliance typically needs 6 inches of clearance and may not pass through floors, ceilings or concealed spaces.
• High-efficiency Category IV appliances vent through the plastic or special vent material their manufacturer specifies.
• On roofs, gas vents 12 inches and smaller that are at least 8 feet from a vertical wall terminate at the heights in IFGC Figure 503.6.5, which is 1 foot above the roof for flat to 6/12 pitches. Larger vents, and vents closer than 8 feet to a wall, must end at least 2 feet above the highest point where they pass through the roof and at least 2 feet above anything within 10 feet horizontally (503.6.5).

Pressure testing and leak checks (IFGC 406)

• Test pressure (406.4.1): at least 1.5 times the maximum working pressure, and at least 3 psig.
• Gauges (406.4): mechanical gauges must have a range whose top is no more than 5 times the test pressure.
• Duration (406.4.2): at least 10 minutes for a single-family dwelling or a system under 10 cubic feet. Otherwise 1/2 hour per 500 cubic feet of pipe volume, but no more than 24 hours.
• Before turning gas on (406.6.2): confirm there are no open ends and all unused outlets are closed and capped. Immediately after turning gas on, check for leaks (406.6.3).

Pipe sizing (IFGC 402)

• Convert each appliance's input to cubic feet per hour: Btu/h ÷ heating value. For natural gas, a 40,000 Btu/h heater needs about 40 cfh. On LP, it needs about 16 cfh.
• In the longest length method, use the length from the meter or second-stage regulator to the most remote outlet. Then read every segment from that one length row in the IFGC sizing table, sizing each segment for the total cfh of all appliances downstream of it.

Exam traps

• 304.6.1 vs. 304.6.2: two openings use 1/4,000 (direct or vertical) or 1/2,000 (horizontal). One opening uses 1/3,000.
• Louvers: wood 25%, metal 75% when unknown.
• Alabama: the gas connection to a gas water heater is gas fitting even beyond the shutoff valve.
• Test pressure: 1.5 times the working pressure and at least 3 psig.