Maryland Master Natural Gas Fitter

Key Concepts

Allowable Pressure & Maximum Operating Pressure (IFGC 101.2.2) - Natural gas systems: max operating pressure 125 psig - LP-gas systems: max operating pressure 20 psig (exceptions per Section 402.7) - Allowable pressure drop for low-pressure systems (under 2 psig): typically 0.5 in. W.C. for longest run; high-pressure systems allow greater drop but must maintain adequate delivery pressure at appliances

Approved Piping Materials (IFGC Chapter 4) - Steel/wrought iron pipe: Schedule 40 black steel is standard; galvanized permitted for certain applications above ground - Copper tubing: Types K and L approved for natural gas; prohibited where gas contains more than 0.3 grains of hydrogen sulfide per 100 SCF - CSST (Corrugated Stainless Steel Tubing): Must be listed per ANSI LC-1/CSA 6.26; requires bonding per IFGC 310.1 and manufacturer installation instructions - Polyethylene (PE) pipe: Approved for underground use only; must be marked per ASTM D2513; minimum SDR 11

Pipe Joints, Fittings & Thread Specifications - Metallic threaded joints: ANSI/ASME B1.20.1 taper pipe threads (NPT); joint compound or tape must be rated for gas service and applied to male threads only - Steel pipe joints may be threaded, welded, or flanged; welding must follow ANSI B31.3 or equivalent - PE pipe joints: heat fusion only (butt or socket); mechanical fittings must be listed for PE gas pipe; solvent cement is prohibited - Flared joints permitted for copper tubing systems

Key Concepts

Pipe Sizing Methods (IFGC Appendix A / Section 402) - Longest Length Method: Size all pipe based on the longest single run from the meter to the farthest appliance. Every pipe segment in the system uses that same total length. Conservative — tends to oversize. - Branch Length Method: Each branch segment is sized based on its own length from the supply point to its specific appliance. More accurate, less material waste. - Hybrid Pressure Drop Method: Uses two pressure drop allowances — a larger drop on the street/service side and a smaller drop on the house piping side. Requires knowing both inlet and minimum delivery pressures.

Pressure Drop Allowances (IFGC A.2.2) - Low-pressure natural gas systems (under 2.0 psig): typical allowable drop is 0.3-inch w.c. (Table 402.4(1)) or 0.5-inch w.c. (Table 402.4(2)) - Minimum delivery pressure at appliance inlet: approximately 5-inch w.c.; appliance regulator delivers ~3.5-inch w.c. to the burner - Source pressure minus allowable drop must still meet minimum appliance inlet pressure

Converting BTU/h to CFH (IFGC A.2.1) - Formula: CFH = Total BTU/h ÷ BTU heating value per cubic foot of gas - Natural gas is typically 1,000 BTU/ft³ (confirm with local supplier) - Example: 80,000 BTU/h appliance ÷ 1,000 BTU/ft³ = 80 CFH

Key Concepts

Appliance Categories (IFGC Chapter 5) - Category I: Non-positive vent pressure, flue gas temp high enough to avoid condensation. Uses Type B vent or masonry with approved liner. Most common residential appliances (furnaces with draft hoods, water heaters). - Category II: Non-positive pressure, may condense. Requires corrosion-resistant venting per manufacturer. - Category III: Positive vent pressure, no condensation. Requires sealed, pressure-rated venting per manufacturer. - Category IV: Positive pressure, condensing. Requires sealed, corrosion-resistant venting per manufacturer (e.g., PVC/CPVC for high-efficiency appliances). - Categories II–IV: Design, sizing, and installation are governed entirely by the appliance manufacturer's instructions (IFGC §501.14) — no generic code tables apply.

Vent Types - Type B: Double-wall metal vent for Category I appliances; most common for natural gas appliances with draft hoods. - Type BW: For Category I wall furnaces (recessed). - Type L: For oil-fired appliances or gas appliances requiring higher temperature ratings. - Single-wall metal pipe: Permitted as vent connectors only; not permitted as a vent itself in most residential applications. Requires minimum 6-inch clearance to combustibles (unless listed for lesser clearance). - Direct-vent (sealed combustion): Draws combustion air from outside; venting sealed from living space. Can terminate horizontally through a wall.

Masonry Chimneys (IFGC §501.3, §503.5.3, §501.12) - Must be lined; acceptable liners: clay tile (ASTM C315), listed chimney lining systems (UL 1777), or other approved materials resistant to 1,800°F (982°C). - Category I appliance liners must also comply with §501.13 (listed for use with gas appliances/Type B vents). - Connectors must enter the flue at least 12 inches above the lowest portion of the interior flue (§501.9). - Cleanout access required; abandoned inlet openings must be sealed (§501.5).

Key Concepts

Combustion Defined: Combustion is the rapid oxidation of fuel (natural gas or propane) producing heat, light, and combustion products (CO₂, water vapor, CO if incomplete). Combustion air is the air supplied to support proper fuel burning.

Flammable Limits: - Natural gas: Lower Flammable Limit (LFL) = 4%, Upper Flammable Limit (UFL) = 14% (gas-to-air by volume). Below 4% = too lean to ignite; above 14% = too rich to ignite. - Propane: LFL = 2.15%, UFL = 9.6%. Propane is heavier than air and settles low — a critical safety distinction.

Standard Indoor Combustion Air Method (IFGC Section 304): - The "standard method" requires 50 cubic feet of indoor volume per 1,000 Btu/h of total appliance input rating. - Example: A 100,000 Btu/h furnace requires 5,000 cu ft of unconfined space volume. - If the space is too small, outdoor combustion air openings are required.

Outdoor Combustion Air – Two-Opening Method (IFGC 304.5.3): - One opening within 12 inches of the ceiling, one within 12 inches of the floor. - Each opening sized at 1 sq in per 4,000 Btu/h of total appliance input if openings communicate directly with outdoors or through vertical ducts. - If horizontal ducts are used: 1 sq in per 2,000 Btu/h.

Outdoor Combustion Air – One-Opening Method (IFGC 304.5.4): - Single opening within 12 inches of the ceiling. - Sized at 1 sq in per 3,000 Btu/h of total appliance input. - Minimum 1 opening, minimum free area of 1 sq in.

Key Concepts

Listing, Labeling & Testing Standards (IFGC Chapter 6) Each appliance type has a specific ANSI/CSA standard. Know these pairings: - Decorative fireplace appliances → ANSI Z21.60/CSA 6.26; manually lighted → ANSI Z21.84 - Vented gas fireplaces → ANSI Z21.50/CSA 2.22 - Vented gas fireplace heaters → ANSI Z21.88/CSA 2.33 - Vented wall furnaces & floor furnaces → ANSI Z21.86/CSA 2.32 - Log lighters → CSA 8

Flame Safeguard Devices (§602.2) Required on decorative fireplace appliances except those tested under ANSI Z21.84 (manually lighted). The device must automatically shut off fuel to the main burner when the ignition source fails. Applies equally to vented gas fireplaces (§604.1) and vented gas fireplace heaters (§605.1).

Vented Wall Furnaces (§608) - Door clearance: No door shall swing within 12 inches of any air inlet or outlet (measured at right angles). Doorstops/closers cannot be used to achieve this clearance. - No ducts may be attached; no casing extension boots unless listed with the appliance. - Cannot circulate air from bathrooms to other building areas.

Floor Furnace Clearances (§609) - Minimum 6-inch clearance from grade (reduced to 2 inches if lower portion is manufacturer-sealed against water). - Register must be ≥6 inches from any wall; ≥18 inches from two adjoining sides to prevent occupants walking over discharge. - Door/drapery must remain ≥12 inches from any part of the register. - Not permitted in concrete floors built on grade, doorways, stairway landings, aisles, or passageways.