Pass the Oklahoma Residential Contractor Plumbing and Natural Gas Exam in 2026
Picture this: you've done the work, built up your skills, and you're ready to make it official with a residential plumbing contractor license in Oklahoma. The one thing standing between you and that credential is the Oklahoma Residential Contractor Plumbing and Natural Gas exam. It's a serious test — 85 scored questions covering everything from isometric drawings to fuel gas safety — but it's absolutely passable with the right preparation. This article walks you through what's on the exam, how it's structured, what study materials you'll need, and how to use your prep time wisely.
Exam Overview
The Oklahoma Residential Contractor Plumbing and Natural Gas exam is administered by PSI and consists of 85 scored questions. You have 180 minutes (3 hours) to complete it.
To pass, you need to answer 75% of questions correctly — that's 64 out of 85. That's a meaningful bar, but it leaves you some room. You don't need to be perfect; you need to be solid.
One important thing to know: this is an open-book exam. You can bring your approved reference materials to the test center. That's a significant advantage — but only if you know your books well enough to find answers quickly. Slow page-flipping burns time, so practice locating information fast before test day.
The exam is computer-based at PSI testing centers. You can bookmark questions to review later during the same session, which is a useful feature to take advantage of. Check the official exam bulletin for the most current details on scheduling and test center locations.
Topics Covered on the Exam
The exam covers ten topic areas. Here's how the 85 scored questions break down — and where to focus the most energy:
- Isometric Analysis — 13 items. The heaviest-weighted topic. Expect reading isometric drawings, calculating offsets, and working through 45-degree constants and fitting allowances. If you're not comfortable with pipe math, start here.
- Fixtures and Equipment — 10 items. Fixture installation standards, water heater requirements, shower compartments, and water closet flushing devices.
- Water Supply — 10 items. Distribution lines, backflow prevention, pressure-reducing valves, thermal expansion, and water hammer arrestors.
- Drains and Sewers — 10 items. Drain fixture units (DFUs), building sewers, cleanouts, and pipe material requirements.
- Safety — 10 items. OSHA construction safety: ladders, fall arrest systems, PPE, and fire prevention. Don't underestimate this section — it's tied for the second-heaviest weight.
- General Plumbing Knowledge and Regulations — 8 items. Code definitions, area/volume calculations, structural member notching and boring rules, and test procedures.
- Piping, Valves, and Control Valves — 8 items. Cast iron, copper, steel, PVC/CPVC/PEX, and connection methods.
- Vents — 7 items. Vent pipe sizing, wet venting, air admittance valves, and termination requirements.
- Traps, Interceptors, Indirect, and Special Waste — 5 items. Trap types, prohibited configurations, ejector pumps, indirect waste, and trap seal protection.
- Fuel Gas — 4 items. Gas piping, valve requirements, supports, pipe sizing, and testing procedures.
When deciding where to focus your study time, follow the item counts above. Isometric Analysis, Safety, Fixtures and Equipment, Water Supply, and Drains and Sewers together account for more than half of the exam.
Sample Questions
Here are five sample questions that reflect the style and difficulty you'll see on the real exam. Work through them and see how you do — but we won't give you the answers here. Take our free practice exam to check your knowledge and get instant feedback.
Question 1 — Piping, Valves, and Control Valves
You are installing a cast-iron drain pipe using 10-foot lengths. What is the maximum horizontal hanger spacing permitted for these pipe lengths?
- A) 4 feet
- B) 5 feet
- C) 15 feet
- D) 10 feet
Question 2 — Fuel Gas
During a safety inspection of an existing gas appliance installation, the combustible gas detector (CGD) reads 20-percent LEL or greater upon entering the building. What action should the inspector take?
- A) Advise the occupant to turn off all gas appliances and schedule a follow-up visit
- B) Shut off the gas supply at the meter and proceed with the appliance inspection
- C) Immediately notify occupants to evacuate, evacuate the building, and call 911
- D) Open all windows and doors and continue the inspection after 15 minutes of ventilation
Question 3 — Piping, Valves, and Control Valves
Water service pipe installed underground and outside a residential structure must have a working pressure rating of not less than what value?
- A) 100 psi at 180°F
- B) 125 psi at 100°F
- C) 160 psi at 73°F
- D) 200 psi at 73°F
Question 4 — Fixtures and Equipment
Flush tanks on water closets are required to be equipped with what type of valve to prevent backflow?
- A) A pressure vacuum breaker assembly
- B) A reduced pressure principle backflow preventer
- C) A dual-check backflow preventer
- D) An antisiphon fill valve
Question 5 — Fuel Gas
What is the distinction between a 'forced draft venting system' and an 'induced draft venting system'?
- A) Forced draft uses natural convection while induced draft uses a fan
- B) Forced draft operates under negative pressure while induced draft operates under positive pressure
- C) There is no difference; both terms describe the same system
- D) Forced draft removes flue gases under positive static pressure, while induced draft removes flue gases under nonpositive static vent pressure
Notice the range: some questions test whether you can recall a specific code requirement, while others — like the gas detector scenario — test your judgment under real-world conditions. Isometric and pipe math questions will require you to work through calculations, so bring your calculator.
What Types of Questions to Expect
Our Oklahoma residential plumbing contractor exam prep pool includes 603 practice questions across all ten topic areas. Here's what each set covers and how many questions we offer:
- General Plumbing Knowledge and Regulations (39 questions): Code definitions, area and volume calculations, structural notching and boring rules, and system testing procedures.
- Piping, Valves, and Control Valves (40 questions): Material-specific installation rules for cast iron, copper, steel, PVC, CPVC, and PEX, plus connection and valve requirements.
- Fixtures and Equipment (48 questions): Water heater installation, fixture clearances, shower receptor specs, and antisiphon requirements for water closets.
- Water Supply (50 questions): Sizing and distribution, potable water protection, backflow prevention methods, pressure-reducing valves, thermal expansion, and water hammer arrestors.
- Drains and Sewers (49 questions): Drain fixture unit calculations, building sewer requirements, cleanout placement, and acceptable drain and water piping materials.
- Vents (35 questions): Vent pipe sizing, developed length limits, wet vent configurations, air admittance valve rules, and termination requirements.
- Traps, Interceptors, Indirect, and Special Waste (25 questions): Trap types and prohibited configurations, ejector pump requirements, indirect waste connections, and trap seal protection methods.
- Isometric Analysis (65 questions): Reading and interpreting isometric drawings, fitting allowances, center-to-end calculations, 45-degree offset constants, and venting system isometrics.
- Fuel Gas (19 questions): Gas piping conduit rules, valve requirements, support spacing, pipe sizing, and pressure testing procedures.
- Safety (50 questions): OSHA 29 CFR 1926 requirements — ladder safety, fall arrest systems, PPE selection and employer responsibilities, and fire prevention programs.
Study Materials
This is an open-book exam, which means the reference books you bring are also your primary study materials. You need to own all three approved references and know them well before test day.
International Residential Code for One-and Two-Family Dwellings (2024) (2018 edition accepted through December 13, 2026) — The 2024 IRC with Oklahoma Revisions is the backbone of this exam. Most plumbing code questions — from fixture requirements to drain sizing to vent terminations — trace back to this book. Tab it heavily by chapter and topic.
OSHA 29 CFR 1926 — The OSHA Standards for the Construction Industry covers the entire Safety section (10 exam items). Don't skip this one. The questions on fall protection, PPE, and ladders come directly from CFR 1926, and knowing where to find specific sections quickly can save you several minutes during the exam.
Mathematics for Plumbers and Pipefitters (8th Edition) — With 13 Isometric Analysis questions on the exam, this book is essential. It covers offset calculations, fitting allowances, 45-degree constants, and the pipe math that shows up throughout the exam. Work through the practice problems — don't just read it.
Your references may be highlighted and tabbed with permanent tabs. They cannot have writing in them, and no loose papers are allowed. Plan your tabbing system before test day so you can locate sections in seconds.
Study Tips
Start early. Give yourself at least three to six weeks. Use the Candidate Information Bulletin as your roadmap and build your study schedule around the topic weights — Isometric Analysis and the 10-item sections deserve the most time.
Practice finding, not just knowing. On an open-book exam, the skill that matters most is getting to the right page fast. Do timed drills where you locate specific code sections in under 60 seconds. The clock still runs while you flip pages.
Set your practice bar at 80%. Aim for three clean practice sessions at 80% or higher before test day. That buffer above the 75% cut score gives you real confidence going in.
Manage test anxiety. A little nervousness is normal. If you get stuck on a tough question, skip it, take a few slow breaths, and come back. Don't let one hard question drain five minutes of your time.
Use the bookmark feature. Answer the questions you know first, bookmark the ones you're unsure about, and circle back. This is exactly how our PSI Oklahoma residential plumbing practice test is structured — so practicing this strategy with us means you're already prepared for the real interface.
Start with our free practice exam to get a feel for the format, then upgrade to the full practice exam for a complete timed simulation with per-topic score breakdowns.
You've Got This
The Oklahoma Residential Contractor Plumbing and Natural Gas exam is thorough, but it's designed to test the knowledge you need to do the job safely and correctly. With the right books, a solid study plan, and consistent practice, 64 out of 85 is well within reach.
Start today: take the free practice exam to see where you stand, then build from there. When you're ready for a full timed simulation with per-topic scoring, the full practice exam has 603 questions waiting for you.