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Oklahoma Residential Contractor Plumbing and Natural Gas — Practice Exam

What This Practice Exam Covers

The Oklahoma Residential Contractor Plumbing and Natural Gas licensing exam is 85 questions with a 180-minute time limit. You need a 75% (64 correct) to pass.

This practice site gives you two ways to prepare:

Free practice exam: 10 questions per attempt, drawn from a limited pool. You can retake it as many times as you want to get a feel for the question format, topic mix, and pacing. It costs nothing and requires no account.

Full practice exam (paid): Mirrors the real exam exactly — 85 questions, 180-minute timer — drawn from a pool of 420+ questions. Every attempt pulls a different set, so retaking it is genuinely useful prep, not memorizing a fixed answer key. Questions are built around the exact topic breakdown provided by the official test provider. If you're serious about passing on your first attempt, this is where to invest your prep time.

Start with the free exam to get oriented, then move to the full exam for serious preparation.

What You'll Be Tested On

The exam covers 10 topic areas with specific item counts. Understanding the weighting helps you prioritize study time.

General Plumbing Knowledge and Regulations (8 items)
Expect math — calculating area and volume of pipes and tanks using formulas from Mathematics for Plumbers and Pipefitters. You'll also need to know general code requirements, definitions from IRC Section R202, rules for notches and holes in structural members, and procedures for testing systems. Water column questions test your understanding of pressure measurement in gas systems.

Piping, Valves, and Control Valves (8 items)
Questions cover material-specific rules across cast iron, copper tubing, steel, PVC/CPVC, and PEX piping — including which joints are permitted for each material, how connections are made, and where specific pipe types may or may not be installed. Valve questions test types, placement requirements, and when full-open valves are mandated.

Fixtures and Equipment (10 items)
This is a high-weight section. Questions address fixture installation clearances, water heater installation requirements (including shut-off valve placement per IRC Section P2903.9.2), shower compartment and receptor dimensions, water closet and flushing device rules, and fixture trap design and sizing. Know the specific requirements for each fixture category — the exam distinguishes between them.

Water Supply (10 items)
Covers water supply and distribution line sizing, protection of potable water, backflow prevention types and placement, pressure-reducing valve requirements, thermal expansion control, and water hammer arrestors. Potable vs. non-potable supply questions (such as which fixtures may use reclaimed water per IRC Section P2901.1) appear here. Pipe material selection and joint requirements for water service are also tested.

Drains and Sewers (10 items)
Drain fixture unit (DFU) values, drain and sewer pipe materials, building sewer requirements, cleanout location and spacing, drainage pipe slope, and joint/connection rules by material type. You must be comfortable reading and applying Table P3004.1 and related DFU tables. Knowing which materials are permitted for building drains vs. building sewers is a common point of failure.

Vents (7 items)
Vent installation rules, wet venting configurations, vent terminal height and location requirements, air admittance valve (AAV) rules, vent pipe sizing, and developed length calculations. Individual vs. common vent distinctions are tested. IRC Sections P3101–P3114 cover most of this material. Appendix N figures (N1–N7) appear directly on the exam for isometric-related vent questions.

Traps, Interceptors, Indirect, and Special Waste (5 items)
Know prohibited trap types, trap sizing requirements by fixture type (Table P3201.7), trap seal protection methods including primer valves and barrier devices, indirect waste requirements, and ejector pump installations. Questions often ask you to distinguish between permitted and prohibited configurations.

Isometric Analysis (13 items)
This is the single heaviest topic on the exam. Questions require reading isometric drawings, calculating fitting allowances (threaded, copper, plastic, welded) using Mathematics for Plumbers and Pipefitters Chapter 1, solving 45-degree offset problems using the 0.707 constant, calculating pipe cut lengths, working with equal spacing, rolling offsets, and interpreting venting isometrics including Appendix N figures. Bring sharp pencil-and-paper skills — multi-step calculations are standard here.

Fuel Gas (4 items)
Gas piping conduit rules, valve placement, support and hanger spacing per IRC sections in Chapter 24, pipe sizing, pressure testing procedures (IRC Section G2417.4.1), and joining methods. Know the prohibited installation locations from IRC Section G2406.2 and bonding requirements.

Safety (10 items)
This section draws heavily from 29 CFR 1926. Topics include construction site safety programs (§1926.20), ladder safety (§1926.1053), fall arrest systems (§1926.502), PPE selection and employer responsibilities (§1926.95), fire protection programs (§1926.150), excavation cave-in protective systems (§1926.652), and asbestos regulations (§1926.1101). Many candidates underestimate this section — it's 10 full items and requires knowing specific OSHA numerical thresholds and requirements.

Worked Sample Questions

Question 1 — Isometric Analysis

You are installing residential plumbing and need to understand the isometric diagrams in the code appendix. Which figure illustrates typical double-bath wet-vent arrangements?

• A. Figure N6
• B. Figure N2
• C. Figure N4
• D. Figure N1

Correct Answer: B — Figure N2

IRC 2018 Appendix N organizes wet-vent figures by configuration type. Figure N1 covers single-bath wet-vent arrangements. Figure N2 is specifically titled "Typical Double-Bath Wet-Vent Arrangements." Figure N4 covers typical methods of wet venting (both vertical and horizontal), and Figure N6 addresses waste stack venting. On the exam, these figure distinctions are tested directly — memorize which figure number corresponds to which configuration.

Source: IRC 2018, Appendix N — Figure N2

Question 2 — Fixtures and Equipment

A readily accessible full-open valve is required on the cold-water supply pipe to each water heater. Where must this valve be installed?

• A. At the water meter
• B. At or near the water heater
• C. At the nearest accessible branch main
• D. At the main water service entrance only

Correct Answer: B — At or near the water heater

IRC Section P2903.9.2 requires that a readily accessible full-open valve be installed in the cold-water supply pipe to each water heater, and it must be located at or near the water heater itself. Placing it at the meter or service entrance does not satisfy this requirement. The "readily accessible" and "at or near" language is specific — the exam tests whether you know both conditions.

Source: International Residential Code, Page 638 (Section P2903.9.2)

Question 3 — Water Supply

Potable water shall be supplied to plumbing fixtures and plumbing appliances, but treated rainwater, treated gray water, or municipal reclaimed water may be supplied to which of the following?

• A. Drinking fountains, kitchen sinks, and lavatories
• B. Kitchen sinks, lavatories, and bathtubs
• C. Water closets, urinals, and trap primers
• D. Showers, bathtubs, and bidets

Correct Answer: C — Water closets, urinals, and trap primers

IRC Section P2901.1 establishes that potable water is required for all plumbing fixtures and appliances, with a specific exception: treated rainwater, treated gray water, or municipal reclaimed water may supply water closets, urinals, and trap primers. No other fixtures in the answer choices qualify for this exception. The question is testing whether you know the precise list of permitted non-potable supply points — not fixtures where water contacts the user's body.

Source: IRC 2018, Section P2901.1

How to Read Your Score

The passing threshold is 75%, which means 64 correct out of 85. On the full practice exam, treat your first attempt as a diagnostic, not a final judgment. A first-attempt score tells you which of the 10 topic areas need more attention — not whether you can or can't pass the real exam.

Topic-by-topic breakdowns are where the real value is. If you score 90% on Safety but 50% on Isometric Analysis, the answer is clear: spend the next study session on 45-degree offset calculations and fitting allowances, not OSHA regulations.

A score of 75–79% on practice should be read honestly: you are at the margin, and margins collapse under real exam pressure. Aim for 85%+ on practice before sitting for the real test. That buffer accounts for questions on the real exam that are worded differently or pull from parts of the code you haven't hit in practice yet.

Retaking the full practice exam is productive because the 420+ question pool means you will encounter new material each attempt. Use each retake to close gaps, not to confirm what you already know.

Where Candidates Lose Points

Isometric Analysis (13 items) is where most candidates hemorrhage points. The 0.707 constant for 45-degree offsets must be second nature. Errors typically come from using the wrong constant, forgetting to subtract fitting allowances from both ends of a pipe cut, or skipping a step in a multi-pipe calculation. Practice the full sequence — offset, diagonal, fitting allowance, cut length — until it is automatic.

DFU values and drain sizing (Drains and Sewers, 10 items) trips candidates who don't know their tables cold. Confusing DFU values between similar fixture types costs real points.

Safety (10 items) catches candidates who skim it. OSHA 29 CFR 1926 questions require specific numerical knowledge — ladder angle ratios, fall protection trigger heights, excavation protective system requirements. Vague familiarity with "ladder safety" is not enough.

Vents (7 items) — candidates lose points by mixing up developed length limits, misidentifying wet vent vs. common vent configurations, or misreading an Appendix N figure reference.

Water Supply backflow questions frequently use terminology precisely. Knowing the difference between an atmospheric vacuum breaker, a pressure-type vacuum breaker, and a reduced-pressure-principle backflow preventer — and where each is required — is non-negotiable.

Finally, time management matters. With 85 questions in 180 minutes, you have about two minutes per question. The isometric math questions can easily eat four or five minutes each if you're not practiced. Know when to flag a question and move on.

Exam Quick Facts