Exam Cheat Sheet · Quick Reference
Maryland Master Natural Gas Fitter
Maryland · PSI Services Contractor
Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
40
Passing score
70%
Exam time
90 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Maryland State Portion 40 questions
General Piping
15 Q · 38%
Allowable pressure drop and maximum operating pressure limitsApproved piping materials and tubing standards (steel, copper, CSST, polyethylene)Pipe joints, fittings, and thread specifications for metallic and plastic pipingPiping system installation requirements (prohibited locations, underground burial depth, protection from physical damage)Pressure testing, inspection, and purging proceduresShutoff valves and flow controls (placement, access, and regulator requirements)Pipe length calculations including fitting allowances and offset geometry
Pipe Sizing/Math
10 Q · 25%
Gas pipe sizing methods (longest length, branch length, hybrid pressure)Pressure drop calculations and allowable loss in gas piping systemsConverting BTU/h appliance demand to cubic feet per hourEquivalent length of pipe fittings and valves for gas systemsFitting allowances for threaded, copper, and welded pipe (center-to-center vs. end-to-end)Offset calculations using trigonometric constants (45°, 60°, 22.5° angles)Pipe volume and capacity calculations (gallons per linear foot, cylinder volume)Grade, drop, and elevation calculations for sloped piping
Chimney and Flues
5 Q · 12%
Types of venting systems and appliance categories (Type B, BW, L, single-wall metal pipe, direct-vent, Category I–IV)Vent and chimney termination location requirementsSizing of Category I appliance venting systems using code tablesVent connector materials, clearances, slope, and installation requirementsMasonry chimney construction, lining, inspection, and cleanout requirementsDraft hoods, draft controls, and automatically operated vent dampersCommon venting and multistory venting system designExit terminal clearances for mechanical draft and direct-vent systems
Combustion
5 Q · 12%
Combustion air requirements for indoor spaces (standard method: 50 cu ft per 1,000 Btu/h)Outdoor combustion air opening sizing and placement methods (one- and two-opening methods)Combination indoor and outdoor combustion air systemsMechanical combustion air supply systems and appliance interlock requirementsLouvers, grilles, and screens: free area calculations and motorized louver interlockingCombustion air duct construction, materials, and installation requirementsDefinitions of combustion, combustion air, combustion products, and related termsFlammable limits and properties of natural gas and propane relevant to combustion safety
Appliances
5 Q · 12%
Listing, labeling, and testing standards for specific appliance typesInstallation clearances to combustible materials for heaters and furnacesUnvented room heater restrictions, input ratings, and oxygen-depletion safety shutoff requirementsClothes dryer exhaust duct materials, length limits, termination requirements, and makeup airCooking appliance installation requirements, clearances, and prohibited locationsSafety inspection procedures for existing appliance installations including CO thresholds by appliance typeFlame safeguard devices and ignition systems for decorative and fireplace appliancesWater heater installation, relief valve requirements, and dual-use space heating applications
Key Distinctions
Appliance shutoff valve in the same room as the appliancevsAppliance shutoff valve installed at a manifold
A same-room shutoff must be within 6 feet of the appliance and upstream of the union, connector or quick-disconnect it serves, while a manifold-mounted shutoff may be up to 50 feet from the appliance served but must be readily accessible and permanently identified.
IFGC 2018 Section 409.5.1Pipe (IFGC 202)vsTubing (IFGC 202)
Pipe is a rigid conduit of iron, steel, copper, copper-alloy or plastic, whereas tubing is a semirigid conduit of copper, copper-alloy, aluminum, plastic or steel (aluminum appears only under tubing).
IFGC 2018 Section 202 (Piping definition)Flared jointvsFlanged joint
A flared joint is a metal-to-metal compression joint where a conical spread on the tube end is compressed by a flare nut against a mating flare, while a flanged joint is made by bolting together a pair of flanged ends.
IFGC 2018 Section 202 (Joint, Flared definition)Mechanical jointvsPlastic heat fusion joint
A mechanical joint is a gas-tight joint made by a positive-holding mechanical construction (press-connect, flanged, threaded, flared or compression), while a plastic heat fusion joint is made in thermoplastic piping by heating the parts enough to fuse them when pressed together.
IFGC 2018 Section 202 (Joint, Mechanical definition)Natural gas systems covered by the codevsLP-gas systems covered by the code
Per IFGC 101.2.2 the code covers natural gas piping operating at 125 psig or less, but LP-gas piping only at 20 psig or less, except as provided in Section 402.7.
IFGC 2018 Section 101.2.2Combustion airvsDilution air
Combustion air is the air necessary for complete combustion of a fuel, including theoretical air and excess air, while dilution air is air introduced into a draft hood and mixed with the flue gases.
IFGC 2018 Chapter 2 DefinitionsGeneral underground gas piping burial depthvsIndividual outdoor appliance line burial depth
Underground piping systems must be at least 12 inches below grade generally, but individual outdoor appliance lines may be installed at 8 inches.
IFGC 2018 Section 404.12Copper tubing Types K, L, M and DWVvsType K specifically
All four types share the same outside diameter for a given nominal size and differ only in wall thickness (and therefore inside diameter); Type K, available in hard and soft temper, is the type recommended for underground water supply service.
Mathematics for Plumbers and Pipefitters (8th ed.), Page 42 (Copper Tubing)Butt-weld fitting allowancevsSocket-weld fitting allowance
Butt-weld fittings require an extra ⅛ inch weld-gap separation added to the fitting allowance (subtracted from end-to-end pipe length), while socket-weld fittings require withdrawing the pipe 1/16 inch from full socket depth to allow for expansion during welding.
Mathematics for Plumbers and Pipefitters (8th ed.), Page 54Long-radius 90° butt-weld elbowvsShort-radius 90° butt-weld elbow and 45° butt-weld elbow
Long-radius 90° elbow allowance is 1½ × pipe size, short-radius 90° elbow is 1 × pipe size (same as a butt-weld tee), and a 45° elbow is ⅝ × pipe size.
Mathematics for Plumbers and Pipefitters (8th ed.), Page 54Cosecant of the fitting anglevsCotangent of the fitting angle
Multiply the offset by the cosecant to find the diagonal (travel), but multiply the offset by the cotangent to find the run/setback; the tangent is used to find the offset from the run.
Mathematics for Plumbers and Pipefitters (8th ed.), Pages 94-96, Unit 25No-Hub cast iron jointvsHubbed cast iron joint
A No-Hub joint uses a gasket enclosed by a stainless steel shield secured with a stainless steel retaining clamp, while hubbed connections use lead and oakum or compression gaskets.
Mathematics for Plumbers and Pipefitters (8th ed.), Page 105 (Unit 27, Cast Iron Pipe)Center-to-center measurementvsEnd-to-end (cut) length
End-to-end is always shorter than center-to-center because the pipe threads into the fitting rather than reaching its center; end-to-end equals center-to-center minus the total fitting allowance.
Mathematics for Plumbers and Pipefitters (8th ed.), Pages 39-41 (Allowance for Threaded Fittings)Key Terms
Piping system IFGC 2018 Section 202 (Piping System definition)
The fuel piping, valves and fittings from the outlet of the point of delivery to the outlets of the appliance shutoff valves.
Pipe IFGC 2018 Section 202 (Piping definition)
A rigid conduit of iron, steel, copper, copper-alloy or plastic.
Tubing IFGC 2018 Section 202 (Piping/Tubing definition)
A semirigid conduit of copper, copper-alloy, aluminum, plastic or steel.
Flared joint IFGC 2018 Section 202 (Joint, Flared definition)
A metal-to-metal compression joint in which a conical spread is made on the end of a tube that is compressed by a flare nut against a mating flare.
Mechanical joint IFGC 2018 Section 202 (Joint, Mechanical definition)
A general form of gas-tight joint obtained by joining metal parts through a positive-holding mechanical construction, such as a press-connect, flanged, threaded, flared or compression joint.
Plastic heat fusion joint IFGC 2018 Section 202 (Joint, Plastic Heat Fusion definition)
A joint made in thermoplastic piping by heating the parts sufficiently to permit fusion of the materials when the parts are pressed together.
Combustion air IFGC 2018 Chapter 2 Definitions
Air necessary for complete combustion of a fuel, including theoretical air and excess air.
Dilution air IFGC 2018 Section 202
Air that is introduced into a draft hood and is mixed with the flue gases.
Longest length method IFGC 2018 Section 402.4.1
A sizing method (IFGC 402.4.1) in which the size of each piping section is determined using the longest length of piping from the point of delivery to the most remote outlet together with the load of the section.
Hybrid pressure method IFGC 2018 Appendix A.3.3
A 2 psi system sizing method (IFGC Appendix A.3.3) in which the maximum allowable pressure drop for the 2 psi section from the meter to the line regulator is 1 psi.
Overpressure protection device IFGC 2018 Section 416.2.1
A device required where gas is supplied above 2 psi to appliances designed for 14 inches w.c. or less; each device must be adjusted to limit pressure to each connected appliance to 2 psi or less upon failure of the line pressure regulator.
MP (medium pressure) regulator IFGC 2018 Section 409.4
A regulator that must have a listed shutoff valve installed immediately ahead of it, and, when indoors, a capped or plugged tee between the regulator and that upstream shutoff valve serving as a pressure-measuring instrument connection and sediment trap.
Internal tubular rigid stiffener (plastic compression joints) IFGC 2018 Section 403.11
A stiffener that must be flush with the pipe end and extend to or beyond the outside end of the compression fitting, be free of rough or sharp edges, not be a force fit in the plastic, and never be of the split tubular type.
Maximum indoor piping operating pressure IFGC 2018 Section 402.7
Piping inside buildings shall not exceed 5 psig unless one of the listed conditions is met (joints welded or brazed; joints flanged with pipe-to-flange connections made by welding or brazing; piping in a ventilated chase or otherwise enclosed; areas used exclusively for industrial processing/heating, research, warehousing, or boiler/mechanical rooms; temporary construction installations; agricultural use; LP-gas systems over 20 psi complying with NFPA 58).
Underground inspection IFGC 2018 Section 107.2
An inspection made after trenches or ditches are excavated and bedded and piping is installed, but before backfill is put in place.
Permit holder (testing responsibility) IFGC 2018 Section 107.3.2
The party required to furnish the apparatus, instruments, material and labor needed to test an installation or part thereof.
Fitting allowance (threaded fitting) Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Pipe Length Calculations
The center-to-face measurement of the fitting minus the thread-in measurement, subtracted (for both ends) from the center-to-center dimension to get the cut length.
Flammable range of natural gas Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 5 (Physics)
Natural gas ignites only in an air-to-gas mixture of about 5 to 15 percent gas; leaner or richer mixtures will not ignite.
Formulas to Know
Appliance gas demand in cubic feet per hour
cfh = total BTU/h input ÷ average BTU heating value per cubic foot (e.g., 150,000 ÷ 1,000 = 150 cfh)Spare (or short) capacity of an installed pipe section
Spare cfh = table capacity for that size and length [Table 402.4(2), <2 psi, 0.5 in. w.c. drop, SG 0.60] − appliance demand cfh (e.g., 170 − 60 = 110; 137 − 80 = 57; 44 − 40 = 4)Minimum pressure-test pressure and duration
Test pressure = 1½ × proposed maximum working pressure, but never less than 3 psig; test duration ≥ 10 minutes for systems under 10 cubic feet or in a single-family dwellingCSST extra fittings/bends equivalent length
L = 1.3n, where L is additional feet of tubing and n is the number of fittings/bends beyond the four 90° bends and two end fittings already in the tableThreaded pipe cut length
End-to-end = center-to-center − total fitting allowance, where each fitting allowance = center-to-face − thread-in (e.g., 24 − [2(1⅛) − 2(½)] = 24 − 1¼ = 22¾ in.)Weld fitting allowances
Long-radius 90° butt-weld ell = 1½ × pipe size; short-radius 90° ell and butt-weld tee = 1 × pipe size; 45° butt-weld ell = ⅝ × pipe size; add ⅛ in. per butt weld for penetration/gap (e.g., 4-in. 45° ell: 4 × ⅝ = 2½ + ⅛ = 2⅝ in.); socket-weld: withdraw pipe 1/16 in. from full socket depthSimple offset constants (diagonal, run, rise from a known offset)
45°: diagonal = 1.414 × offset, offset = 0.707 × diagonal; 30°: diagonal = 2.000 × offset, run = 1.732 × offset; 60°: diagonal = 1.155 × offset, run = 0.5774 × offset, rise = 0.577 × offsetRolling offset and 45° parallel offset
True offset = √(offset² + rise²) (e.g., √(12² + 9²) = 15 in.), then diagonal = true offset × the fitting-angle constant; for 45° parallel offsets, difference in length between the two diagonals = 0.414 × spreadIndoor combustion air volume and combined indoor/outdoor reduction
Standard method: required volume = (total Btu/h ÷ 1,000) × 50 cu ft (e.g., 180,000 Btu/h → 9,000 cu ft); combination method: outdoor opening reduction factor = 1 − (available indoor volume ÷ required volume), openings sized at that fraction of the full Section 304.6 sizeGrade, drop and elevation for pipe runs
Drop = grade × run (¼ in./ft × 40 ft = 10 in. = 0.833 ft, so high end = 95.00 + 0.833 = 95.83 ft); percent grade: drop = (percent × run) ÷ 100 (1% × 60 ft = 0.60 ft); grade = drop ÷ run (5 in. ÷ 22 ft = 0.227 in./ft ≈ 7/32 in./ft)