Maryland Journey Natural Gas Fitter

(15 questions, 38% of exam — highest-weighted topic)

Key Concepts

Allowable Pressure & Maximum Operating Pressure

• Indoor piping systems: Maximum operating pressure is 0.5 psig (14 inches water column) for most residential/commercial systems. Systems above 0.5 psig require special design considerations and approved materials.
• Allowable pressure drop: For low-pressure systems, the maximum allowable pressure drop from meter to appliance is typically 0.5 inch water column for systems operating at 7–14 in. WC.

Approved Piping Materials

• Steel pipe: Black steel, Schedule 40 (standard weight) — the most common material for gas piping. Galvanized steel is prohibited for gas interior piping (zinc reacts with gas).
• Copper: Only permitted where the gas is not corrosive; not permitted for LP gas in some jurisdictions. Must be Type K or L hard-drawn copper.
• CSST (Corrugated Stainless Steel Tubing): Must be installed per manufacturer's listing and bonded/grounded per NFPA 54 requirements. Requires arc-fault bonding to minimize lightning damage risk.
• Polyethylene (PE): Approved for underground use only. Must be yellow-jacketed and marked. Never install PE above ground or inside buildings.
• Aluminum: Prohibited in exterior locations where it may be in contact with certain soils; not permitted in some gas applications — verify local code.

Weight: 10 questions, 25% of exam. This is the highest-yield topic. Master it.

Key Concepts

Gas Pipe Sizing Methods - Longest Length Method: Size all pipe segments based on the single longest run from the meter to the farthest appliance. Conservative and simple — one table lookup covers the whole system. - Branch Length Method: Size each branch segment using only the length of that specific branch from its last tee to the appliance. More efficient, allows smaller pipe in shorter runs. - Hybrid Pressure Method: Uses different allowable pressure drops (e.g., higher drop = smaller pipe acceptable). Applied where system operates above standard low-pressure (under 2 psi).

Maximum Gas Demand (CFH) - Convert appliance BTU/hr ratings to cubic feet per hour (CFH): CFH = BTU/hr ÷ heating value of gas - Natural gas heating value: 1,000 BTU per cubic foot (standard assumption) - Example: A 100,000 BTU furnace = 100,000 ÷ 1,000 = 100 CFH - Total system demand = sum of all appliance CFH ratings served by that segment

Pressure Drop Allowances - Standard low-pressure systems (under ½ psi supply): allowable pressure drop typically 0.3 in. W.C. to 0.5 in. W.C. - Higher-pressure systems allow greater drop, enabling longer runs or smaller pipe - Equivalent length of fittings must be added to actual pipe length before sizing

Equivalent Length for Fittings - Every fitting adds resistance equal to a length of straight pipe — called equivalent length - Add equivalent lengths of all elbows, tees, valves, and other fittings to actual measured pipe length to get total equivalent length - Total equivalent length is used to look up pipe size in sizing tables

Key Concepts

Appliance Venting Categories Gas appliances fall into four categories based on flue gas temperature and pressure: - Category I: Non-positive vent pressure, flue temp not likely to cause condensation (most common — uses Type B vent or masonry) - Category II: Non-positive pressure, may condense - Category III: Positive pressure, unlikely to condense - Category IV: Positive pressure, likely to condense Categories II–IV must be vented per the appliance manufacturer's instructions (IFGC §501.14). Do not apply standard venting tables to these.

Gas Vent Types - Type B: Double-wall metal vent for Category I appliances with draft hoods; most common residential application - Type BW: Used with wall furnaces - Type L: For appliances burning liquid petroleum or high-temperature applications - Single-wall metal pipe: Limited use; greater clearances to combustibles required

Vent Connector Requirements (IFGC §503) - Must slope upward toward the chimney — minimum ¼ inch per foot rise - Maximum horizontal length limits apply (generally no more than 75% of the vertical height of the chimney or vent above the connector inlet) - Single-wall connectors require larger clearances to combustibles than Type B - Connectors must enter a masonry chimney flue not less than 12 inches above the lowest interior point of the flue (§501.9)

Masonry Chimney Requirements - Must be lined — acceptable liners include clay tile (ASTM C315), listed chimney lining systems (UL 1777), or other approved materials resisting up to 1,800°F (§501.12) - Category I appliance flue liners must comply with §501.13 (same clay/listed liner or Type B-rated liner) - Constructed and sized per IBC; utilized per IFGC §501.11 and manufacturer instructions

Key Concepts

Combustion Air: Indoor vs. Outdoor Methods (IFGC Section 304)

• Indoor (conventional) method: Air is drawn from inside the building. Requires a minimum of 50 cubic feet of volume per 1,000 Btu/h of total appliance input. If the space is too small, openings to adjacent interior spaces are required.
• Outdoor method: Air is ducted directly from outside the building. Two openings required — one within 12 inches of the ceiling, one within 12 inches of the floor. Each opening must have a minimum free area of 1 in² per 4,000 Btu/h of total input for direct outdoor openings, or 1 in² per 2,000 Btu/h when communicating with the outdoors through vertical ducts.
• All openings must be permanently open or equipped with automatic openers interlocked with the appliance.

Combustion Air Opening Sizing

Flammability Limits (LEL/UEL)

• Natural gas: Lower Explosive Limit (LEL) = 5%, Upper Explosive Limit (UEL) = 15% in air
• Propane: LEL = 2.15%, UEL = 9.6% in air
• Combustion/ignition only occurs within these limits. Below LEL = too lean to ignite; above UEL = too rich to ignite.
• Propane has a wider lower flammability threshold (ignites at a lower concentration), making leaks more immediately dangerous at smaller volumes.

Key Concepts

Listing, Labeling & Testing Standards

Each appliance type has a specific testing standard — memorize these pairings: - Decorative appliances (in fireplaces): ANSI Z21.60/CSA 6.26; manually lighted → ANSI Z21.84 (§602.1) - Vented gas fireplaces: ANSI Z21.50/CSA 2.22 (§604.1) - Vented gas fireplace heaters: ANSI Z21.88/CSA 2.33 (§605.1) - Vented wall furnaces & floor furnaces: ANSI Z21.86/CSA 2.32 (§608.1, §609.1) - Log lighters: CSA 8 (§603.1)

Flame Safeguard & Ignition Devices

Per §602.2, decorative fireplace appliances (except those tested to ANSI Z21.84) must use a direct ignition device, ignitor, or pilot flame and be equipped with a flame safeguard device that automatically shuts off fuel when the ignition means becomes inoperative. This same requirement applies to vented gas fireplaces (§604.1) and vented gas fireplace heaters (§605.1).

Unvented Room Heaters

• Maximum input: 40,000 BTU/hr for residential use
• Must have an oxygen-depletion safety shutoff (ODS) system
• Prohibited locations: bedrooms, bathrooms, and any room that must pass through a bedroom or bathroom to exit

Clothes Dryer Exhaust Ducts

• Material: rigid or flexible metal duct — no plastic
• Maximum length: 35 feet from dryer to termination, reduced by 2.5 feet per 45° elbow and 5 feet per 90° elbow
• Termination: must exhaust to outside the building, never into attic, crawlspace, or concealed space
• Duct must have a backdraft damper at the termination