- OK-MECH here refers specifically to the Oklahoma Mechanical Trade License Exam for HVACR Contractor Unlimited.
- The Oklahoma Construction Industries Board oversees licensing; PSI Services LLC delivers the computer-based exam.
- The trade exam is 90 questions in 240 minutes, and you need 70% correct to pass.
- "Unlimited" requires documented experience on equipment above 25 tons and 500,000 Btu/h.
What OK-MECH Actually Stands For
On this site, OK-MECH is shorthand for the Oklahoma Mechanical Trade License Exam - HVACR Contractor Unlimited. It is not a generic national HVAC badge and it is not a catch-all term for every mechanical credential that happens to share a similar name. It refers to one specific trade examination administered under Oklahoma's mechanical licensing framework, scoped to the Unlimited HVAC/R contractor classification.
That distinction matters because "OK-MECH" gets used loosely in search results and forum posts to describe several different things. If you're researching this exam, you want to be certain the facts you're reading - fees, question counts, domains, eligibility - actually apply to the Oklahoma trade exam and not to an unrelated program that happens to share initials. For a broader introduction to the credential itself, see What Is OK-MECH?, and for a plain-language breakdown of the letters themselves, check What Does OK-MECH Stand For?
Who Governs and Grades the Exam
Two organizations sit behind the name. The Oklahoma Construction Industries Board (CIB) is the state agency that sets licensing rules, reviews applications, and issues the mechanical contractor license once you've cleared both required exams. PSI Services LLC is the third-party testing provider that builds, delivers, and scores the computer-based exam at authorized test centers.
This two-party structure is common in state trade licensing: the board decides who is eligible and what the license means, while the testing vendor handles the mechanics of question delivery, timing, and scoring on exam day. When you register, you're scheduling through PSI; when you apply for the license itself, you're dealing with the CIB.
The current PSI candidate bulletin governing this exam is effective August 31, 2026, and it's the authoritative source for exact question content, allowed references, and testing-day rules. If you want a section-by-section explanation of that bulletin translated into plain English, the OK-MECH Study Guide 2026: How to Pass on Your First Attempt walks through it in more depth.
Why "Unlimited" Changes Everything
The word "Unlimited" in the credential's full name is not decorative. Oklahoma's mechanical licensing structure includes different contractor scopes, and the Unlimited classification is defined by capacity thresholds, not just trade category. To qualify under this classification, applicants must document qualifying hands-on work on equipment rated above 25 tons and 500,000 Btu/h - meaning commercial and industrial-scale systems, not just residential split systems and small package units.
This is a meaningful filter on who this exam is actually for. It targets technicians and prospective contractors whose field experience already includes larger commercial refrigeration, rooftop units, boiler plants, and industrial ductwork - not entry-level residential installers. If your background is exclusively small residential systems, you'll want to review the OK-MECH Requirements 2026: Eligibility, Prerequisites & How to Qualify article closely before scheduling, since the experience documentation requirement is strict.
Key Takeaway
Don't apply for the Unlimited exam based on trade title alone - the CIB wants proof of hands-on work above the 25-ton / 500,000 Btu/h threshold, verified through experience certifications and, where applicable, school records.
The Six Domains Behind the Name
Every letter in "HVACR Contractor Unlimited" is represented in the content outline the CIB and PSI use to build the trade exam. The 90 scored questions are distributed across six official subject areas, and the distribution is deliberately uneven - some domains carry far more weight than others.
Domain 1: Electrical Knowledge and Controls - 15 questions
Covers the electrical fundamentals and control logic a mechanical contractor must apply on the job, from circuit basics to component-level control troubleshooting.
- Motor and control circuit fundamentals
- Component-level diagnostics tied to HVAC/R systems
Domain 2: Natural Gas - 12 questions
Focuses on gas-fired equipment installation and venting requirements under the applicable fuel-gas code.
- Gas piping sizing and venting principles
- Combustion and appliance clearance rules
Domain 3: Air Distribution Systems - 25 questions (largest domain)
This is the single heaviest domain on the exam, nearly triple the size of the smallest one. Duct design, airflow, and distribution equipment questions dominate here.
- Duct sizing and layout principles
- Airflow balancing and distribution equipment
Domain 4: Refrigeration and Air Conditioning Systems - 20 questions
The second-largest domain, reflecting the core refrigeration cycle knowledge expected of an Unlimited-level contractor.
- Refrigeration cycle and system components
- Commercial-scale AC system principles
Domain 5: Heating Systems - 15 questions
Covers combustion heating equipment and system design beyond gas-specific code questions in Domain 2.
- Heating equipment types and applications
- System design and efficiency considerations
Domain 6: Safety - 3 questions
The smallest domain by question count, but not one to skip, since safety references (including OSHA material) are part of the allowed open-book resources.
- Jobsite and equipment safety practices
- Referenced OSHA safety material
For a deeper walkthrough of each domain with more topic-level detail, see the OK-MECH Exam Domains 2026: Complete Guide to All 6 Content Areas. Because Air Distribution Systems and Refrigeration/AC together account for 45 of the 90 questions - half the exam - your preparation time should be weighted accordingly rather than spread evenly across all six areas.
Exam Format, Fees, and Registration
The trade exam itself is 90 computer-based questions delivered in a 240-minute window, with 70% required to pass. PSI may insert up to 10 additional unscored experimental questions into the exam; these don't count toward your score, and the time spent answering them doesn't count against your official testing time.
A separate Business and Law examination is also required for licensure - 50 questions in 120 minutes, also requiring a 70% passing score. Both portions must be passed within three years of eligibility approval under CIB rules, and each attempt costs its own fee.
| Item | Detail |
|---|---|
| Trade exam fee (per attempt) | $92 |
| Business and Law exam fee (per attempt) | $92 |
| Trade exam format | 90 questions, 240 minutes, 70% to pass |
| Business and Law format | 50 questions, 120 minutes, 70% to pass |
| Initial CIB application/license payment | $330 ($30 application + $300 license) |
| Annual license renewal fee | $200, due in birth month |
Retakes have mandatory waiting periods: 30 days after a first failed attempt, and 90 days after any subsequent failure. For the exact numbers behind these fees and how they add up across the full licensing process, see OK-MECH Certification Cost 2026: Complete Pricing Breakdown, and for the scoring mechanics specifically, review OK-MECH Passing Score 2026: Exactly What You Need to Pass. Current scheduling windows and deadlines relative to the August 31, 2026 bulletin are covered in OK-MECH Exam Dates 2026: Testing Windows, Deadlines & Scheduling.
Note the code-edition transition built into the current bulletin: the 2024 IMC and IFGC become usable September 14, 2026, while the 2018 editions stop being allowed December 14, 2026 - meaning there's an overlap window where either edition may still be in play. Similarly, Modern Refrigeration and Air Conditioning, 22nd edition, became usable August 13, 2026, and its 20th edition along with Refrigeration and Air Conditioning Technology, 5th edition, are phased out November 1, 2026. Bring the correct edition for your test date.
Who Is Actually Eligible
Candidates must be at least 18 years old and meet the mechanical journeyman experience requirements plus one additional qualifying year, on top of being an owner, partner, officer, or permanent employee of a mechanical firm. The standard experience-only route totals four years, though approved education can reduce the journeyman experience component required to get there.
Documentation matters as much as the experience itself. Applicants need experience certifications and, where relevant, school records to support their application - and for the Unlimited scope specifically, that documentation needs to show work on equipment above the 25-ton / 500,000 Btu/h threshold discussed earlier. This is worth reviewing carefully before you pay any exam fee, since eligibility denial after payment wastes both time and money. The requirements article covers each qualifying path in more detail.
What the Name Means After You Pass
Passing the trade exam and the Business and Law exam doesn't automatically hand you an active contractor license - it clears the testing requirement. Active contractor licensing under the CIB also requires a $5,000 surety bond and $50,000 commercial general liability insurance in place before the license becomes active.
Once licensed, renewal is annual, tied to your birth month, at a $200 contractor renewal fee. Continuing education is required at six approved hours every 36 months, though there's an initial three-year examination exemption built into the renewal cycle. In other words, "OK-MECH" doesn't describe a one-time test - it describes an ongoing licensing relationship with the state that starts with the exam but continues through bonding, insurance, and periodic renewal.
If you're weighing whether pursuing this credential is worth the combined cost of exams, bonding, insurance, and renewal, Is the OK-MECH Certification Worth It? Complete ROI Analysis 2026 lays out the considerations. For what the license can open up on the employment side, see OK-MECH Jobs and OK-MECH Salary Guide 2026: Complete Earnings Analysis.
Turning the Definition Into a Study Plan
Understanding what OK-MECH stands for is only useful if it shapes how you prepare. Because the domain weighting is so uneven - Air Distribution Systems at 25 questions and Refrigeration/AC at 20 questions together make up half the exam, while Safety carries only 3 - a generic study schedule that treats every topic equally will waste your limited prep time.
Heavy Domains First
- Build core competency in Air Distribution Systems and Refrigeration/AC Systems
- Work through duct sizing, airflow balancing, and refrigeration cycle problems
Mid-Weight Domains
- Cover Electrical Knowledge and Controls, Heating Systems, and Natural Gas
- Practice reading code excerpts under open-book conditions
Consolidation and Safety
- Review Safety domain material and OSHA reference structure
- Run full-length timed practice sessions using allowed references only
Practicing under realistic timing matters given the 240-minute window and the open-book reference rules - knowing where a fact lives in your reference material is often faster than memorizing it outright. A structured question bank built around these six domains is one of the most efficient ways to get that repetition in before test day; you can start practicing on the main practice test platform to get a feel for the question style and pacing. For a condensed, single-page reference of the numbers covered in this article, see the OK-MECH Cheat Sheet 2026: One-Page Review of Must-Know Facts, and if you want a candid read on overall exam difficulty before committing to a study timeline, check How Hard Is the OK-MECH Exam? Complete Difficulty Guide 2026.
Key Takeaway
Spend disproportionately more prep time on Air Distribution Systems and Refrigeration/AC Systems - together they're half the exam - rather than dividing study hours evenly across all six domains.
Frequently Asked Questions
It refers to the Oklahoma Mechanical Trade License Exam - HVACR Contractor Unlimited, the trade portion of Oklahoma's mechanical contractor licensing process administered through the Oklahoma Construction Industries Board and tested via PSI Services LLC.
No. The trade exam (90 questions, 240 minutes) and the Business and Law exam (50 questions, 120 minutes) are separate examinations, each with its own $92 fee, and both must be passed for licensure.
Unlimited applicants must document qualifying work on equipment above 25 tons and 500,000 Btu/h, distinguishing this scope from smaller residential-focused classifications within Oklahoma's mechanical licensing structure.
Air Distribution Systems, which accounts for 25 of the 90 scored questions - the largest single domain by a wide margin over Safety's 3 questions.
You still need a $5,000 surety bond and $50,000 commercial general liability insurance before the CIB activates your contractor license, plus the $330 initial application/license payment.