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Oklahoma Plumbing Contractor and Natural Gas — Practice Exam

What This Practice Exam Covers

This practice exam targets the Oklahoma Plumbing Contractor and Natural Gas licensing exam: 85 questions, 180-minute time limit, 75% passing score.

Free practice exam: 10 questions per attempt, drawn from a limited question pool. You can retake it as many times as you want to get familiar with the question style, format, and pacing — no purchase required.

Full practice exam: Mirrors the real exam exactly — 85 questions, 180-minute timed session. Questions are pulled from a pool of 447+ items, so each attempt produces a different exam. No two sessions are identical, which means repeated attempts build genuine knowledge rather than answer memorization. Questions are built from the exact topic blueprint provided by the official test provider.

Start with the free exam to benchmark where you stand, then use the full exam for the serious repetition that builds passing-level confidence.

What You'll Be Tested On

The exam covers 10 topic areas. Weights are fixed by the official blueprint.

General Plumbing Knowledge and Regulations — 10 items
Expect questions on IPC scope and intent, permit applications, and what work is exempt from permits. The code official's inspection authority matters here, as do the specific types of required inspections — underground, rough-in, and final. Per IPC 2018, Page 8 (Section 107.2), the final inspection occurs after the building is complete and all fixtures are connected. You also need pipe math: fitting allowances for threaded, copper, and PVC joints, and offset/diagonal calculations using angle constants (45°, 60°, and others).

Piping, Valves, and Control Valves — 8 items
Know joint types and approved connection methods for gas and water piping. Water supply pipe materials and their applicable standards appear here, along with valve types — pressure-reducing valves, backflow preventers, and relief valves — and where each is required. Piping support and hanger spacing from IPC 2018, Chapter 3, Table 308.5 is testable. Center-to-center and end-to-end pipe length calculations with fitting allowances are common.

Fixtures and Equipment — 8 items
This section requires knowing minimum fixture counts by occupancy from IPC 2018, Table 403.1 and Section 403.1.1. Individual fixture clearances, water closet and urinal standards, and trap requirements are all in play. Water heater safety devices, including T&P relief valves (IPC 2018, Sections 504.4.1 and 504.6), appear regularly. Shower valves and temperature-limiting controls are also tested here.

Water Supply — 10 items
A high-weight section. Backflow prevention devices and correct application — reduced pressure assemblies, double check valves, pressure vacuum breakers — must be matched to hazard type. Cross-connection control, potable water identification, and pipe material selection are critical. Per IPC 2018, Page 80–81 (Section 608.17.4), labeling of nonpotable systems is required. Pressure booster systems, water hammer arrestors, and thermal expansion control round out the section.

Drains and Sewers — 10 items
Drainage pipe material standards for above-ground versus underground versus building sewer installations (IPC Chapter 7, Tables 702.1 and 702.3) are directly tested. Fixture unit loading values from Section 709.1 and Table 709.1, pipe sizing, and minimum slope for horizontal drainage (Section 704.1, Table 704.1) are frequently examined. Cleanout locations and spacing rules (Sections 708.1.1 through 708.1.11), sumps, ejectors, and backwater valve requirements complete this area.

Vents — 13 items
The heaviest section on the exam. Vent pipe sizing, developed length limits, and the differences among individual, common, wet, circuit, and island fixture venting methods are all testable. Know vent terminal heights above roofs, clearances from operable openings, and wall termination rules (IPC 2018, Chapter 9, Sections 903.1, 903.5, 903.6). Air admittance valve installation conditions and prohibited locations (Sections 918.2 through 918.8) are high-probability questions. Relief vent connections (Section 908.2) and combination waste-and-vent systems also appear.

Traps, Interceptors, Indirect, and Special Waste — 10 items
Trap seal depth, prohibited trap types (Section 1002.1 and its exceptions), and trap primer requirements (Section 1002.4.1.1 through 1002.4.1.4) are all tested. Grease interceptor sizing and automatic grease removal device rules (Sections 1003.3.1 through 1003.3.8) are commonly examined. Indirect waste piping rules, the distinction between air gap and air break (Chapter 8, Sections 802.1.1 through 802.1.6), standpipes, and waste receptors also appear.

Isometric Analysis — 7 items
Pure math. Given an isometric diagram, you calculate center-to-center distances and then subtract fitting allowances to get end-to-end pipe lengths. The 45° offset uses the 1.414 diagonal multiplier and the 0.707 offset multiplier (Mathematics for Plumbers and Pipefitters, Pages 107–109). Three-pipe offset diagrams add a rise component. Multi-fitting assemblies with wyes, tee-wyes, and elbows require systematic step-by-step arithmetic — careless arithmetic is the biggest risk here.

Fuel Gas — 5 items
Gas pipe sizing methods — longest length, branch length, and hybrid pressure — and approved piping materials (steel, copper, CSST, polyethylene) per the 2018 IFGC are tested. Pressure requirements, allowable pressure drop, venting system sizing, and combustion air supply methods (indoor, outdoor, mechanical) all appear. Appliance location and clearance rules from the 2018 IFGC (Oklahoma) are also in scope.

Safety — 4 items
OSHA 29 CFR 1926 rules govern this section. The 6-foot fall protection trigger (§1926.501(b)(1)), guardrail height and load requirements (§1926.502(b)(1) and §1926.502(b)(5)), personal fall arrest system specifications (§1926.502(d)(3)), and ladder safety rules are all testable. PPE provision and selection (§1926.95(b) and §1926.95(d)(1)) and safety net system requirements (§1926.502(c)(4)(i)) round out the section.

Worked Sample Questions

Question 1 — Vents

Where must the upper end of a relief vent for a soil or waste stack in a building with more than 10 branch intervals connect to the vent stack?

• A. At the same elevation as the horizontal branch it serves
• B. Not less than 6 inches above the flood level rim of the highest fixture on that floor
• C. Through a wye not less than 3 feet above the floor
• D. At or below the lowest horizontal branch on the floor

Correct Answer: C

The connection must be made through a wye, and that wye must be positioned not less than 3 feet (914 mm) above the floor. The lower end connects to the soil or waste stack through a wye below the horizontal branch serving that floor. Answer B sounds plausible because flood level rim measurements appear elsewhere in the code, but that specific measurement does not govern this connection — the 3-foot-above-floor wye requirement does.

Source: IPC 2018, Chapter 9 — Section 908.2

Question 2 — General Plumbing Knowledge and Regulations

Which required plumbing inspection must be performed after the building is complete, all plumbing fixtures are in place and properly connected, and the structure is ready for occupancy?

• A. Rough-in inspection
• B. Final inspection
• C. Preliminary inspection
• D. Underground inspection

Correct Answer: B

The IPC defines four inspection stages. The rough-in inspection happens before walls are closed; the underground inspection happens before backfill. Only the final inspection is triggered when the building is complete, all fixtures are installed and connected, and the structure is ready for occupancy. "Preliminary inspection" is not a defined IPC inspection type and is a distractor.

Source: International Plumbing Code 2018, Page 8 (Section 107.2)

Question 3 — Water Supply

What is the minimum height above all downstream piping and outlets at which a pressure vacuum breaker assembly must be installed?

• A. 12 inches
• B. 6 inches
• C. 18 inches
• D. 24 inches

Correct Answer: A

The critical level of a pressure vacuum breaker assembly must be located not less than 12 inches above all downstream piping and outlets. The 6-inch figure appears in other backflow preventer rules and is a common wrong-answer trap here. The 18-inch and 24-inch values appear in other clearance contexts but not this one.

Source: Uniform Plumbing Code, Section 608.14.5

How to Read Your Score

The passing score on the real exam is 75% — 64 correct out of 85 questions.

Treat your first practice attempt as a diagnostic, not a verdict. A score in the 50s tells you which topic clusters need the most work, not that you cannot pass. A score of 70–74% on a first full attempt is encouraging but not safe — the real exam draws from the same knowledge base with different question wording, and a few uncertain guesses that landed right in practice may not land right on exam day.

Use the topic-by-topic breakdown after each attempt. If you score below 75% in Vents (13 items) or Drains and Sewers (10 items), those gaps alone can sink your overall score because of their weight. Fuel Gas and Safety together account for only 9 items — time spent on Vents or Water Supply almost always returns more points.

Scoring consistently above 80% across multiple full attempts — not just one — is the realistic indicator that you are ready. Each full practice attempt draws from 447+ questions, so a second or third attempt will surface new questions and expose gaps that a single run might have missed.

Where Candidates Lose Points

Vent sizing and connection rules — This single topic is 13 items, more than 15% of the exam. Candidates who blur the difference between individual, common, wet, and circuit venting, or who cannot locate the correct vent terminal clearance rule, lose multiple points in one section.

Isometric math errors — The 7-item Isometric Analysis section is entirely calculation-based. The most common mistake is applying the 1.414 diagonal multiplier correctly but then forgetting to subtract fitting allowances for both ends of each pipe segment. Skipping one step costs the whole question.

Wrong backflow preventer for the hazard — Water Supply has 10 items and tests whether you can match the correct device to the application. Pressure vacuum breakers, reduced pressure assemblies, and double-check assemblies are not interchangeable. Mixing them up — especially on the minimum installation height — is a consistent point-loss pattern.

Misreading drainage slope tables — Candidates sometimes apply the correct slope value (e.g., 1/4 inch per foot) to the wrong pipe size, or confuse building drain sizing rules with branch sizing rules. IPC Chapter 7, Section 704.1 and Table 704.1 govern this precisely.

Running out of time — 180 minutes for 85 questions averages just over 2 minutes per question. Multi-step calculations in Isometric Analysis and pipe sizing questions in Water Supply and Drains can each consume 4–5 minutes. Practice under timed conditions on the full 85-question exam so that time pressure does not become the reason you leave questions blank.

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