Exam Cheat Sheet · Quick Reference

Oklahoma Residential Contractor Plumbing and Natural Gas

Oklahoma  ·  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
85
Passing score
75%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed

Oklahoma State Portion 85 questions

General Plumbing Knowledge and Regulations 10 Q · 12%
Calculate Area and VolumeGeneral Code RequirementsPlumbing DefinitionsNotches and Holes in Structural MembersTest SystemsWater ColumnPipe OffsetsPiping support requirements and spacing by material typeProtection of piping from physical damage, corrosion, and freezingTrenching, bedding, and backfilling requirementsPipe penetrations, waterproofing, and sealing of annular spacesMaterials identification, listing, and third-party certification +7 more
Piping, Valves, and Control Valves 8 Q · 9%
Piping ConnectionsCast Iron PipingCopper Piping and TubingSteel PipingPVC, CPVC, Plastic and PEX PipingValvesBackflow Prevention Devices and AssembliesWater Supply System Design and Pipe SizingPressure Requirements and Pressure-Reducing ValvesPipe Support Spacing and Installation RequirementsPipe Length Calculations and Fitting AllowancesDrainage Pipe Sizing and Slope Requirements +3 more
Fixtures and Equipment 8 Q · 9%
Fixture InstallationInstall Water HeatersRequirements for FixturesShower Compartment and Receptor RequirementsWater Closet and Flushing Device RequirementsFixture Trap Design and SizingBackflow Prevention Devices and ApplicationsTemperature and Pressure Relief Valves for Water HeatersWater Heater Location and Safety RequirementsBoiler Safety Controls and Operating RequirementsGas Appliance Installation and Clearance RequirementsFixture Standards and Material Requirements +4 more
Water Supply 10 Q · 12%
Water Supply and Distribution LinesProtection of Potable Water SupplyBackflowWater supply system pressure requirements and pressure-reducing valvesThermal expansion control and water hammer arrestorsPipe and tubing materials, joints, and connections for water service and distributionValves and shutoff requirements for water service and fixturesWater supply fixture units and pipe sizing methodsNonpotable water systems identification, storage, and distributionWater heater installation, relief valves, and safety requirementsDwelling unit fire sprinkler system water supply and pipe sizingWater service pipe separation from building sewer +7 more
Drains and Sewers 10 Q · 12%
Drain and Sewer PipeBuilding SewersSewer and Drain CleanoutsDFUsDrain and Water PipingDrainage pipe joints and connections by material typeHorizontal drainage piping slope requirementsDrain pipe sizing using fixture unit loads and tablesCleanout installation requirements and clearancesBackwater valvesSumps and sewage ejectorsDWV system testing procedures +7 more
Vents 13 Q · 15%
Vent InstallationWet VentingVent terminals and termination requirementsAir admittance valvesVent pipe sizing and developed lengthIndividual and common ventsCircuit ventingCombination waste and vent systemsWaste stack ventingIsland fixture ventingTrap seal protection and pressure differential limitsVent grades, connections, and drainage of condensate +6 more
Traps, Interceptors, Indirect, and Special Waste 5 Q · 6%
Ejector PumpsIndirect WasteTrapsTrap seal protection methods (primer valves and barrier devices)Prohibited trap typesTrap sizing requirements by fixture typeNumber of fixtures per trap and double-trapping prohibitionGrease interceptors and separatorsBackwater valvesSumps and ejector design requirementsTrap seal depth requirements (minimum and maximum liquid seal)Trap design and material construction standards +2 more
Isometric Analysis 7 Q · 8%
Isometric DrawingsFitting Allowances and Center-to-End CalculationsOffset, Diagonal, Rise, and Run Relationships45-Degree Offset Constants and Pipe Length CalculationsReading and Interpreting Venting System IsometricsEqual Spacing and Pipe Cut ListsParallel Offset CalculationsGrade, Drop, and Elevation in Plan View DiagramsRolling Offsets and True Offset CalculationsJumper Offsets Using 45° and 90° FittingsCombination Offsets (45° and 60° Fittings)Trigonometric Constants for Non-45° Offset Angles +3 more
Fuel Gas 10 Q · 12%
Gas Piping ConduitGeneral Gas Piping and ValvesPiping Supports and HangarsPipe SizingTestingInstallation and Joining Gas PipeThreadsCombustion air requirements and methodsAppliance location and clearances to combustiblesVenting systems and vent typesElectrical bonding of gas piping (CSST and metallic pipe)Appliance connectors and shutoff valves +11 more
Safety 4 Q · 5%
Construction ActivitiesLaddersFall Arrest SystemsPersonal Protective Equipment (PPE) selection, use, and employer responsibilitiesFire protection and prevention programsExcavation hazards and cave-in protective systemsFirst aid, medical services, and emergency responseHousekeeping and site sanitation requirementsHazardous substances and permissible exposure limitsEmployer safety training and accident prevention responsibilitiesGuardrail system specifications and load requirementsSafety net system installation, testing, and inspection +6 more

Key Distinctions

Soil stack (soil pipe)vsWaste pipe (waste stack)

A soil stack conveys sewage containing fecal material, while a waste pipe conveys only liquid sewage that does not contain fecal material.

IRC 2024 Chapter 2
Atmospheric-type vacuum breakervsPressure vacuum breaker assembly

The atmospheric vacuum breaker's critical level must be set not less than 6 inches above the highest downstream piping and the fixture flood level rim, whereas a pressure vacuum breaker assembly requires not less than 12 inches.

IRC 2024 Section P2902.3.2
45°/60° combination offset — standard positionvs45°/60° combination offset — alternate position

In the standard position rise = offset and setback = 1.414 × offset; in the alternate position rise = 1.414 × offset and setback = offset (diagonal = 2 × offset in both).

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Combination Offsets
Center-to-center (c-c) lengthvsEnd-to-end (e-e) length

Equal spacing makes c-c lengths equal, but e-e lengths differ when fitting types differ (e.g., 90° ell vs. 45° ell) because fitting allowances differ; e-e is always c-c minus the total fitting allowance.

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 1 — Equal Spacing
Threaded fitting allowancevsCopper solder-cup / PVC fitting allowance

Threaded allowance is center-to-face minus thread-in (extra calculation steps for thread-in), while copper and PVC allowance 'G' is center-to-face minus the depth of the solder/close-tolerance cup.

Mathematics for Plumbers and Pipefitters (8th ed.), Page 44
RisevsRun

For parallel vertical pipes the distance between them is called the rise; for parallel horizontal pipes that same dimension is called the run ('set' is a shortened form of 'offset').

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Offset, Diagonal, Rise, and Run
Horizontal drainage piping 3 inches or largervsHorizontal drainage piping 2½ inches and smaller

Piping 3 inches or more requires a uniform slope of not less than ⅛ unit vertical in 12 horizontal (1 percent), while piping 2½ inches and less requires not less than ¼ unit vertical in 12 horizontal (2 percent).

IRC 2024 Section P3005.3
Cubic (volume) measurevsSquare (area) measure

One cubic foot = 1,728 cubic inches (12×12×12) and tells how much a container holds, while one square foot = 144 square inches (12×12) and describes the size of a surface to be covered; linear measure is only distance.

Mathematics for Plumbers and Pipefitters (8th ed.), Unit 1 (Section 1, Review of Basic Fundamentals, Cubic or Volume Measure)
Wet ventvsCircuit vent / combination waste-and-vent

A wet vent vents one or more fixtures while also carrying the discharge of another fixture (classic single bathroom group), whereas circuit vents serve batteries of fixtures and combination waste-and-vent is a different, more restricted system.

Vacuum breakervsBackwater valve / pressure-relief valve / air admittance valve

A vacuum breaker prevents backsiphonage by admitting atmospheric pressure through ports on the discharge side, unlike a backwater valve (prevents backflow of sewage), a pressure-relief valve (relieves excess pressure), or an air admittance valve (admits air into the drainage system).

IRC 2024 Section R202
Fuel-piping systemvsFlue collar / vent connector

The fuel-piping system is all piping, tubing, valves and fittings connecting fuel utilization equipment to the point of fuel delivery, while the flue collar and vent connector belong to the venting system, not the fuel-piping system.

IRC 2024 Section R202
Individual water supplyvsApproved public water supply

An individual water supply is a supply other than an approved public water supply that serves one or more families; the definition exists specifically to distinguish it from a public supply.

IRC 2024 Chapter 2
Pipe invert elevationvsPipe centerline measurement

Most pipe is measured to the centerline, but sewers and house drains show elevations measured to the invert (inside bottom) of the pipe.

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Elevation in a Plan View Pipe Diagram
T and P valvevsStandalone pressure-relief or temperature-relief valve

A T and P valve is a combination relief valve designed to function as both a temperature-relief and a pressure-relief valve, while each standalone valve addresses only one condition.

IRC 2024 Section R202

Key Terms

Slip joint IRC 2024 Section R202
A mechanical-type joint used primarily on fixture traps in which tightness is obtained by compressing a friction-type washer (rubber, nylon, neoprene, lead or special packing) against the pipe by tightening a slip nut.
Plumbing fixture IRC 2024 Section R202
A receptacle or device connected to a water supply system or discharging to a drainage system, or both.
Supply fitting IRC 2024 Section R202
A category of fixture fitting that controls the volume or directional flow (or both) of water and is attached to or accessed from a fixture or used with an open/atmospheric discharge.
Vacuum breaker IRC 2024 Section R202
A device that prevents backsiphonage of water by admitting atmospheric pressure through ports to the discharge side of the device.
Steam heating boiler IRC 2024 Section G2403
A boiler in which steam is generated and that operates at a steam pressure not exceeding 15 psig.
Direct-vent appliance IRC 2024 Section R202
A fuel-burning appliance with a sealed combustion system that draws all combustion air from the outside atmosphere and discharges all flue gases to the outside atmosphere.
Combustion air IRC 2024 Section R202
Air provided to fuel-burning equipment including air for fuel combustion, draft hood dilution, and ventilation of the equipment enclosure.
Fuel-piping system IRC 2024 Section R202
All piping, tubing, valves and fittings used to connect fuel utilization equipment to the point of fuel delivery.
Individual water supply IRC 2024 Chapter 2
A supply other than an approved public water supply that serves one or more families.
Temperature- and Pressure-Relief (T and P) valve IRC 2024 Section R202
A combination relief valve designed to function as both a temperature-relief and a pressure-relief valve.
Branch interval IPC 2021 Section 202 (Branch interval)
A vertical length of stack of 8 feet or more between the connections of horizontal branches; branches connecting less than 8 feet apart fall within the same branch interval.
Wet vent
A pipe that vents one or more fixtures while also carrying the discharge of another fixture, typically within a single bathroom group.
Fitting allowance (threaded) Mathematics for Plumbers and Pipefitters (8th ed.), Page 39
The distance between the end of the pipe (which may be inside the fitting) and the center of the fitting, i.e., center-to-face minus thread-in, used to convert c-c to e-e length.
Diagonal (travel) Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Offset, Diagonal, Rise, and Run
The center-to-center length of the connecting pipe where two parallel pipes are joined by fittings other than 90°; the diagonal is preferred because there is less restriction to flow.
Invert Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Elevation in a Plan View Pipe Diagram
The inside bottom of a pipe, the solid surface to which sewer and house drain elevations are measured.
Cut-in fitting (valve) Mathematics for Plumbers and Pipefitters (8th ed.), Page 38
A fitting such as a valve installed into a straight line of pipe, for which two fitting allowances (one on each side of the valve) must be accounted for in the center-to-center measurement.
Self-siphoning fixture (water closet) IPC 2021 Table 909.1
A fixture, such as a water closet, whose trap-to-vent distance is not limited by the maximum trap arm distances printed for other trap sizes.

Formulas to Know

Static (gauge) pressure from water headStatic pressure = vertical height of water above the point × 0.433 psi/ft (e.g., 46 ft × 0.433 = 19.9 ≈ 20 psi; 60 ft × 0.433 ≈ 26 psi). Pressure difference between two fixtures uses only the elevation difference between them, not tank height (38 ft − 6 ft = 32 ft; 32 × 0.433 ≈ 13.9 psi).
Height of water column needed for a given pressureHeight = pressure ÷ 0.433 psi/ft (20 ÷ 0.433 = 46.2 ft; 30 ÷ 0.433 = 69.3 ft) — divide, do not multiply.
Total fall/drop of graded drainage and invert elevationsFall = grade (in/ft) × run (ft); 12 in = 1.00 ft. Examples: ¼ in/ft × 18 ft = 4½ in; ⅛ in/ft × 32 ft = 4 in; 48 ft × ¼ in/ft = 12 in = 1.00 ft. Downstream invert = upstream invert − total fall (100.00 − 1.00 = 99.00 ft; 101.00 − 0.92 = 100.08 ft). Rising up-grade: ⅛ in ≈ 0.01 ft, so 0.01 × 25 ft = 0.25 ft added (91.55 + 0.25 = 91.80 ft).
Grade expressed as percent slopePercent slope = (rise in inches per foot ÷ 12 in per foot) × 100; ¼ in/ft = (0.25 ÷ 12) × 100 = 2.08%.
Cut (end-to-end) length of threaded and solder/solvent pipeThreaded: e-e = c-c − (takeoff/center-to-face × number of fittings) + (thread engagement × number of ends) = c-c − total fitting allowance. Examples: 10 − [2(1⅛) − 2(½)] = 8¾ in; 42 − (2 × 2¼) + (2 × ½) = 38½ in; 36 − (2 × 2) + (2 × ½) = 33.00 in; thread engagement adds ½ in per end = 1 in for two ends. Copper/PVC: allowance G = center-to-face − depth of cup; sweat fittings deduct ½ in per fitting end (24 − 1 = 23 in; 18 − 1 = 17 in).
Volume and capacity of a cylindrical tank / pipeV = π r² h with r = diameter ÷ 2 (18 in dia., 30 in tall: 3.14 × 9² × 30 ≈ 7,630 in³; 4 ft dia., 6 ft tall: π × 2² × 6 = 75.4 ft³; half-full = use half the height). Gallons = cubic feet × 7.5 (80 ft³ × 7.5 = 600 gal) or × 7.48 (37.7 ft³ × 7.48 = 282 gal; 100 ft of 2-in ID pipe: π × (1/12)² × 100 = 2.18 ft³ × 7.48 = 16.3 gal).
Simple offset constants (parallel pipes)45° offset: travel (diagonal) = set × 1.414 and run = set × 1.000 (9 in × 1.414 = 12.73 in; 20 in × 1.414 = 28.28 ≈ 28¼ in; run = 20 in). 22½° offset: travel = set × 2.613 (10 × 2.613 = 26.13 ≈ 26⅛ in; 20 × 2.613 = 52.26 ≈ 52¼ in). 60° fittings: travel = offset × 1.155.
Rolling offset true offset and travelTrue offset = √(set² + roll²) = √(12² + 9²) = √225 = 15.0 in (3-4-5 family); then travel = true offset × fitting constant (45°: 15.0 × 1.414 = 21.2 in; 60°: 15.0 × 1.155 = 17.3 in). Same Pythagorean rule finds a hypotenuse: √(15² + 20²) = 25 ft.
Minimum size of an individual vent (IPC 2021 Section 906.2)Vent size = ½ the diameter of the fixture drain served, but never less than 1¼ in; if the vent's developed length exceeds 40 ft, increase one nominal size for its entire length. Examples: 1½ in drain → 0.75 → 1¼ in (1½ in if over 40 ft); 2 in drain → 1 in → 1¼ in (1½ in if over 40 ft); 3 in drain → 1½ in.
Maximum allowable friction loss rate for pipe sizingAllowable friction rate = (available pressure ÷ total equivalent length of the longest run, including fittings) × 100 = (22 psi ÷ 250 ft) × 100 = 8.8 psi per 100 ft.
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