Exam Cheat Sheet · Quick Reference
Maryland Journey Natural Gas Fitter
Maryland · PSI Services Contractor
Maryland State Portion 40 questions
Key Distinctions
Flue gases are combustion products plus excess air in appliance flues or heat exchangers, whereas combustion products are the constituents resulting from combustion of fuel with oxygen (including inert gases) but exclude excess air.
IFGC 2018 Chapter 2 DefinitionsWhere the design and free area are not known, wood louvers are assumed to have 25% free area while metal louvers and grilles are assumed to have 75% free area (screens not smaller than 1/4-inch mesh).
IFGC 2018 Chapter 3 General Regulations, Section 304.10Pipe is a rigid conduit of iron, steel, copper, copper-alloy, or plastic, while tubing is a semirigid conduit of copper, copper-alloy, aluminum, plastic, or steel.
IFGC 2018 Section 202, DefinitionsA pressure test verifies the gas-tight integrity of gas piping following installation or modification, while a leak check verifies that the system does not leak (typically during or after placing in service).
IFGC 2018 Section 202, DefinitionsA pressure test verifies gas-tight integrity after installation or modification, whereas purging frees a gas conduit of air or gas, or a mixture of gas and air.
IFGC 2018 Section 202, DefinitionsThe code covers natural gas piping systems operating at 125 psig or less, but LP-gas piping systems only at 20 psig or less (except as provided in Section 402.7).
IFGC 2018 Section 101.2.2Indoor piping systems must not exceed 5 psig unless a listed condition is met, such as welded/brazed joints, piping in a ventilated chase or otherwise enclosed against accidental gas accumulation, industrial/warehouse/boiler rooms, temporary installations, or agricultural use; residential kitchens, finished basements, and cast-iron threaded fittings are not qualifying conditions.
IFGC 2018 Section 402.7Bored hole diameter in joists must not exceed one-third the member depth (and not within 2 inches of top or bottom), while bored holes in wood studs must not exceed 40 percent of stud depth (60 percent allowed only in nonbearing partitions or doubled studs under certain conditions).
IFGC 2018 Section 302.3.2Underground piping systems must be at least 12 inches below grade; the reduced 8-inch depth is allowed only for individual lines to outdoor lights, grills, and similar appliances under specific conditions.
IFGC 2018 Section 404.12A service shutoff valve is installed by the serving gas supplier between the meter/source of supply and the customer piping system to shut off the entire system, while an appliance shutoff valve must be in the same room as the appliance, within 6 feet of it, and upstream of the union, connector, or quick-disconnect it serves.
IFGC 2018 Section 202, DefinitionsTable equivalent-length values are calculated for steel pipe and may be used with reasonable accuracy for copper/copper-alloy fittings and bends, but for copper or copper-alloy valves the equivalent length must be taken as 45 percent longer than the listed values.
IFGC 2018 Appendix A, Section A.3.1Cast-iron pipe shall not be used for gas piping, while steel pipe (Schedule 10 or heavier), copper tubing, and CSST are permitted under appropriate conditions; aluminum-alloy pipe is permitted but not in exterior locations or underground, and copper/copper alloy may not be used where the gas contains more than an average of 0.3 grains of hydrogen sulfide per 100 standard cubic feet.
IFGC 2018 Section 403.4.1Key Terms
Formulas to Know
CFH = total BTU/h input ÷ heating value (BTU per cubic foot); e.g., 75,000 ÷ 1,000 = 75 CFH. Where appliance ratings are unknown, use the approximate consumption values in Table 402.2.Spare cfh = table capacity of the installed pipe size at that length − appliance demand (Table 402.4(2), Schedule 40 metallic, <2 psi inlet, 0.5 in. w.c. drop, SG 0.60); e.g., 247 − 35 = 212 cfh; 137 − 80 = 57 cfh; 44 − 40 = 4 cfh; 117 − 40 = 77 cfh.Add equivalent length whenever a run has four or more fittings: total = number of fittings × table equivalent length (e.g., 6 × 2.62 ft = 15.72 ft for screwed 90° ells on 1-in. Sch 40; 4 × 2.41 ft = 9.64 ft for screwed 45° ells on 2-in. Sch 40). For copper or copper-alloy valves, take equivalent length as 45% longer than the table values.45°: diagonal = offset × 1.414 (10 × 1.414 = 14.14 in.). 60°: diagonal = offset × 1.1547 (10 × 1.1547 ≈ 11.55 in.); run = diagonal × 0.5000 (24 × 0.5 = 12 in.); run = offset × 0.5774 (18 × 0.5774 = 10.39 in.). 30°: diagonal = offset × 2.000 (14 × 2 = 28.00 in.).True offset = √(rise² + horizontal offset²); e.g., √(6² + 8²) = √100 = 10 in.; then apply the fitting-angle constant to get the diagonal.Drop = grade × run (¼ in./ft × 18 ft = 4½ in.); Grade = drop ÷ run (10 in. ÷ 50 ft = 0.20 in./ft); Percent grade = (drop ÷ run) × 100 with drop and run in the same units (8 in. = 0.667 ft; 0.667 ÷ 60 × 100 ≈ 1.1%; 3.5 ft ÷ 200 ft × 100 = 1.75%).Pressure = 0.434 psi × height in feet (0.434 × 42 ft ≈ 18.2 psi); Height = 2.304 ft × psi (2.304 × 25 = 57.60 ft); based on water weighing 62.5 lb per cubic foot.Pipe volume shortcut: V (gal) = 0.0408 × d²(in.) × h(ft) → 0.0408 × 3² × 8 ≈ 2.94 gal (a 1-in. dia., 1-ft long cylinder holds 0.0408 gal). Weight = 62.5 lb/cu ft × cu ft (15 × 62.5 = 937.5 lb). 1 gal water ≈ 8.33 lb; 1 U.S. gal = 231 cu in.; 1 cu ft = 12 × 12 × 12 = 1,728 cu in.Multiply the decimal by 16 and round when the next digit is 5 or greater: 0.375 × 16 = 6/16 = 3/8 in.; 0.725 × 16 = 11.6 → 12/16 = 3/4 in.; 1.78 ft × 12 = 21.36 in., 0.36 × 16 = 5.76 → 6/16 = 21 3/8 in.Threaded: allowance per fitting = center-to-face − thread-in (1⅛ − ½ = ⅝ in.), end-to-end = c-c − total allowance (10 − 1¼ = 8¾ in.). Copper: e-e = c-c − sum of fitting allowances (10 − (½ + ¼) = 9¼ in.). Butt-weld elbows: long-radius 90° = 1½ × pipe size (1.5 × 4 = 6 in.), short-radius 90° = 1 × pipe size (6-in. pipe = 6 in.), 45° = ⅝ × pipe size (⅝ × 8 = 5 in.), and reduce e-e an additional ⅛ in. per butt-weld fitting for the weld gap (3-in. pipe: 24 − 2[(1.5 × 3) + 0.125] = 14¾ in.).