Gas Appliances and Piping

Learning Objectives

By the end of this chapter, you will be able to:

4.Identify the scope and jurisdictional boundaries between the International Plumbing Code (IPC) and the International Fuel Gas Code (IFGC) regarding gas piping and appliance installation.

5.Determine minimum gas pipe sizing using the longest length method and the branch length method, including the application of tables and pressure drop calculations.

6.Apply the requirements for gas appliance venting, combustion air, and appliance connections, including the distinction between Category I, II, III, and IV appliances.

7.Recognize the Maryland-specific amendments and licensing responsibilities that affect a master plumber's work on gas systems.

8.Navigate the open-book exam efficiently by locating key tables, definitions, and structural safety requirements within the 2018 codes.

1.1 Scope and Code Hierarchy

The 2018 International Plumbing Code (IPC) governs the installation, alteration, and repair of plumbing systems, including the water supply and distribution piping that serves gas appliances indirectly (e.g., condensate drains, relief valve discharge). However, the fuel gas piping system itself—from the point of delivery to the appliance connection—is governed by the 2018 International Fuel Gas Code (IFGC). Maryland adopts both codes with state-specific amendments. As a master plumber, you are responsible for knowing when each code applies.

Point of delivery is a critical term. For natural gas, it is the outlet of the utility meter or the point of connection to the service line. For LP-gas, it is the outlet of the first-stage regulator or the tank connection. Piping upstream of this point is the utility's responsibility; downstream is yours.

Maryland regulations require that a master plumber supervise all gas piping installations. Even if a journeyman performs the work, the master is the responsible licensed individual. This means your signature on the permit application certifies code compliance, not just workmanship.

1.2 Gas Piping Materials and Joints

The IFGC Chapter 4 (Gas Piping Installations) specifies acceptable materials. The most common for residential and light commercial work are:

Black steel pipe (Schedule 40) with threaded fittings.

Corrugated stainless steel tubing (CSST) — must be installed per the manufacturer's installation instructions and the specific bonding requirements of the code.

Polyethylene (PE) pipe — allowed only for underground exterior piping, never inside a building.

Copper tubing — allowed only if the gas does not contain more than trace amounts of hydrogen sulfide, and only with brazed joints (not solder). This is a frequent exam trap.

Joint requirements: Threaded joints must be made with a pipe thread compound that is resistant to the action of LP-gas (if applicable). Do not use hemp or other fibrous materials. Flared joints are permitted with CSST and certain metallic tubing. Mechanical joints must be installed per the manufacturer's listing.

Prohibited locations: Gas piping may not be installed in or through a duct, a chimney, an elevator shaft, or a garbage chute. It may be embedded in a concrete floor slab only if it is protected against corrosion and is not subject to expansion or contraction. Piping in a hollow wall or partition is allowed, but access must be provided for inspection if the piping is not continuous.

1.3 Pipe Sizing: The Longest Length Method

The IFGC provides two sizing methods: the longest length method (also called the branch length method) and the summation method. The longest length method is the most commonly tested and used in practice.

Procedure:

28.Determine the gas demand for each appliance in British thermal units per hour (Btu/h).

29.Convert each appliance demand to cubic feet per hour (cfh) by dividing by the heating value of the gas (approximately 1,000 Btu/ft³ for natural gas; check local utility values).

30.Determine the equivalent length of the piping system from the point of delivery to the farthest appliance. Add 50% for fittings (or use the actual fitting equivalent lengths from Table 6.2.4 if you want precision—the 50% rule is a conservative approximation accepted by many inspectors).

31.Select the appropriate sizing table (IFGC Chapter 6, Tables 6.2.4 through 6.2.8) based on:

Gas type (natural or LP).

Pressure (low pressure ≤ 0.5 psi or high pressure > 0.5 psi).

Pressure drop (typically 0.3-inch water column for low-pressure systems, 0.5-inch for longer runs).

Specific gravity of the gas.

36.Using the total equivalent length and the total demand of the system, select a pipe size for the main line. Then, for each branch, use the demand of that branch and the length from the point of delivery to the farthest appliance served by that branch (not the total system length) to size the branch.

Common error: Sizing every branch based on the total system demand. The branch must carry only the load of the appliances it serves, but the length used is the distance to the farthest appliance on that branch, not the branch's own physical length if it is shorter.

Pressure drop: For low-pressure natural gas systems, the allowable pressure drop from the meter to the appliance is typically 0.5-inch water column (w.c.) for the entire system, with 0.3-inch w.c. allowed for the piping alone if the appliance regulator accounts for the rest. The tables in the IFGC are based on a 0.3-inch w.c. drop for low-pressure systems; a 0.5-inch drop table is also provided. Know which table you are using.

1.4 Gas Appliance Connections

Each appliance must be connected to the gas piping by a rigid metallic pipe or an appliance connector listed for the application. The connector must not pass through any wall, floor, or ceiling. A shutoff valve must be installed in the piping within 6 feet of the appliance, upstream of the connector, and must be accessible.

Drip legs (sediment traps) must be installed where the gas piping changes direction to rise to the appliance, unless the appliance is designed to prevent sediment from entering. The drip leg must be a capped nipple at least 3 inches long, sized to the pipe, and installed in a vertical position.

Appliance pressure regulators are required on appliances with manifold pressures above the appliance rating. The regulator must be accessible and vented to the outdoors if the gas is LP-gas (because of the higher specific gravity and the danger of pooling).

Union connections: A union or flanged connection must be provided adjacent to each appliance to allow disconnection for service. This is not just a convenience—it is a code requirement.

1.5 Combustion Air and Venting

The IFGC Chapter 7 (Combustion Air) requires that each gas appliance have sufficient air for complete combustion and for venting. The standard rule is 50 cubic feet of space per 1,000 Btu/h of appliance input for rooms that are not directly vented to the outdoors. If the space is confined (less than 50 ft³ per 1,000 Btu/h), you must provide outdoor air.

Two openings method: If using the "two permanent openings" method, each opening must have a free area of at least 1 square inch per 4,000 Btu/h of total appliance input, with a minimum of 100 square inches. One opening must be within 12 inches of the ceiling, the other within 12 inches of the floor.

One opening method: A single permanent opening is allowed if it is located within 12 inches of the ceiling and has a free area of 1 square inch per 3,000 Btu/h. The opening must communicate directly with the outdoors or through a vertical duct.

Venting: The IFGC Chapter 8 (Venting) classifies appliances by their venting characteristics:

Category I: Negative pressure in the vent, non-condensing. Typical atmospheric draft water heaters.

Category II: Negative pressure, condensing.

Category III: Positive pressure, non-condensing. Requires sealed vent connectors.

Category IV: Positive pressure, condensing. High-efficiency furnaces and boilers.

Vent sizing for Category I appliances uses Tables 8.4.2.1 through 8.4.2.4, which account for the vent height, the lateral connector length, and the total Btu/h input. The vent connector must be the same size as the appliance draft hood outlet unless the table permits a reduction (rare) or an increase (allowed under specific conditions).

Common trap: A vent connector serving two appliances must be sized for the combined input, and the smaller appliance must connect at the higher elevation (above the larger appliance's connector) to prevent backdrafting.

1.6 Appliance Installation and Clearances

The IFGC Chapter 3 (General Regulations) requires that appliances be installed with clearances from combustible materials as specified by the manufacturer's listing, or per Table 3.1.3 if the appliance is not listed. Standard clearances for unlisted appliances are typically 6 inches from the top, 6 inches from the sides, and 6 inches from the back, but these vary by appliance type.

Appliance location: Gas appliances must not be installed in a bathroom or bedroom unless they are of the direct-vent type or are listed for such installation. This is a common code violation in residential remodels.

Leveling and protection: Appliances must be level and must be protected from physical damage. A water heater in a garage must be elevated so the ignition source is at least 18 inches above the floor, to reduce the risk of igniting gasoline vapors.

1.7 Shutoff Valves and Pressure Testing

Every appliance must have an individual shutoff valve. In addition, a main shutoff valve must be installed at the point of delivery. For multi-tenant buildings, each tenant space must have its own shutoff valve.

Pressure testing (IFGC Chapter 4, Section 4.2) requires that the piping system be tested at 10 psi for a minimum of 30 minutes, with no perceptible drop, before the system is placed in service. If the system includes appliances, the test is performed with the appliance shutoff valves closed and the appliance disconnected or isolated. For systems operating at pressures above 0.5 psi, the test pressure must be at least 1.5 times the operating pressure, but not less than 10 psi.

Leak check: After the pressure test, a leak check is performed with a manometer or soapy water at all joints while the system is under normal operating pressure. Never use an open flame to detect leaks.

1.8 Maryland-Specific Amendments and Licensing

Maryland adopts the IPC and IFGC with amendments published in the Code of Maryland Regulations (COMAR). Key points for the exam:

The State Board of Plumbing requires that a master plumber hold a license for the jurisdiction where the work is performed. A master plumber may supervise multiple journeymen, but the ratio and notification requirements vary by local jurisdiction.

Maryland does not adopt the IFGC appendix chapters unless specifically referenced. Do not rely on appendices for exam answers unless the question references a Maryland amendment.

Backflow prevention on gas appliance water connections (e.g., water heaters) is governed by the IPC, not the IFGC. A master plumber must ensure that the cold water inlet to a water heater has a backflow preventer or a check valve if required by local ordinance.

1.9 Code Navigation: Where to Find It

Concept	Code Location
Definitions (point of delivery, appliance, vent)	IFGC Chapter 2 (Definitions)
Gas piping materials and joints	IFGC Chapter 4, Sections 4.4–4.6
Pipe sizing tables	IFGC Chapter 6, Tables 6.2.4–6.2.8
Appliance connections and shutoff valves	IFGC Chapter 4, Section 4.7
Combustion air requirements	IFGC Chapter 7, Sections 7.1–7.3
Venting of appliances	IFGC Chapter 8, Sections 8.1–8.5
Appliance clearances	IFGC Chapter 3, Section 3.1 and Table 3.1.3
Pressure testing	IFGC Chapter 4, Section 4.2
Water heater relief valves and discharge	IPC Chapter 5, Section 504
Condensate disposal for high-efficiency appliances	IPC Chapter 8, Section 814
OSHA excavation and trenching (for underground gas lines)	29 CFR 1926 Subpart P

1.10 Practical Field Points for the Master Plumber

80.Bonding CSST: The 2018 IFGC requires that CSST be bonded to the electrical grounding electrode system with a minimum 6 AWG copper conductor. This is a frequent point of inspection failure and a liability issue—an unbonded CSST system can be punctured by a lightning strike, causing a fire.

81.Relief valve discharge: For a gas-fired water heater, the temperature and pressure relief valve discharge pipe must terminate a maximum of 6 inches above the floor, must not be threaded at the end, and must not be connected to the sanitary drainage system. This is an IPC requirement, not IFGC, but you are responsible for both.

82.Condensate neutralization: High-efficiency condensing appliances produce acidic condensate. The IPC requires neutralization before discharge to the sanitary drainage system if the local authority requires it. Many Maryland jurisdictions do require this.

83.Permit and inspection: As the master plumber, you must pull the permit, schedule the inspections, and be present (or ensure a licensed journeyman is present) for the rough-in and final inspections. The gas test is typically performed by the installer, but the inspector will witness the test or require a signed certification.

1.11 Common Exam Traps

Trap 1: Sizing a branch line with the total system load. Always use the load of the branch, not the whole house.

Trap 2: Using the wrong pressure drop table. Low-pressure natural gas tables assume 0.3-inch w.c. drop. If the question states a 0.5-inch drop is allowed, use the corresponding table.

Trap 3: Confusing Category III and IV. Category III is positive pressure, non-condensing; Category IV is positive pressure, condensing. Both require sealed vent systems, but only Category IV produces condensate.

Trap 4: Allowing a gas appliance in a bedroom. Unless it is direct-vent or listed for bedroom installation, it is prohibited.

Trap 5: Forgetting the 18-inch elevation in garages. This applies to the ignition source, not the base of the appliance. A water heater with a top-mounted burner may not need 18 inches of elevation if the ignition source is above that height.

Trap 6: Using solder on copper gas piping. Only brazed joints are allowed.

Trap 7: Testing with air at operating pressure. The code requires a 10 psi test, not just a leak check with soapy water.

1.12 Summary

The gas piping and appliance content on the Maryland Master Plumber exam is heavily weighted toward the IFGC, but the IPC governs the plumbing connections to those appliances. Master the sizing tables, understand the venting categories, and memorize the key clearance and testing numbers. In the open-book exam, your ability to navigate to the correct table quickly is as important as your knowledge of the rules. Practice locating each table in your own copy of the code before exam day, and mark the most frequently used pages with tabs.

Remember: The exam is not testing your ability to memorize the code—it is testing your ability to find and apply the correct requirement under time pressure. Your reference book is your tool; know how to use it.

Gas Appliances and Piping