- What the OK-MECH Trade Exam Actually Tests
- Registration, Fees, and Eligibility Mechanics
- Exam Format: Questions, Timing, and Scoring
- Domain-by-Domain Breakdown (90 Questions)
- What You Can Bring: Open-Book References and Rules
- A Six-Week Study Timeline Built Around the Domains
- Retakes, Business & Law, and Renewal Realities
- Frequently Asked Questions
- The HVACR Contractor Unlimited trade exam has 90 questions in 240 minutes, and you need 70% to pass.
- Air Distribution Systems carries 25 of 90 questions - the single largest domain on the test.
- The trade exam costs $92 per attempt; Business and Law is a separate $92 exam with 50 questions.
- Unlimited applicants must document experience on equipment above 25 tons and 500,000 Btu/h.
What the OK-MECH Trade Exam Actually Tests
OK-MECH, in the context of this site, refers specifically to the Oklahoma Mechanical Trade License Exam for the HVACR Contractor Unlimited classification - one trade portion within Oklahoma's broader mechanical contractor licensing system, administered by the Oklahoma Construction Industries Board (CIB) and delivered on computer through PSI Services LLC. It is not a general HVAC certificate or a manufacturer credential; it is a state licensing exam tied directly to your legal ability to contract HVAC/R work in Oklahoma without tonnage or Btu/h limits.
If you're still confirming what this credential covers before diving into study mode, it's worth reading What Is OK-MECH? and OK-MECH Meaning first. This guide assumes you already know you're pursuing the Unlimited contractor trade exam and want a concrete, exam-specific path to a first-attempt pass.
Registration, Fees, and Eligibility Mechanics
Before you can register with PSI, the CIB has to approve your application. The eligibility path is not just "years on the job" - it's structured:
- You must be at least 18 years old.
- You must meet the mechanical journeyman experience requirements, plus one additional year of qualifying experience specific to the contractor level.
- You must be an owner, partner, officer, or permanent employee of a mechanical firm - not an independent applicant with no company affiliation.
- The standard experience-only route totals four years, though approved education can reduce the journeyman experience component.
For the full eligibility breakdown, including how experience certifications and school records factor in, see OK-MECH Requirements 2026: Eligibility, Prerequisites & How to Qualify.
Once you're approved to test, the fee structure looks like this:
| Item | Cost |
|---|---|
| Trade exam (HVACR Contractor Unlimited) | $92 per attempt |
| Business and Law exam (separate, also required) | $92 per attempt |
| Initial CIB application fee | $30 |
| Initial CIB license fee | $300 |
| Total initial application/license payment | $330 |
| Annual contractor license renewal | $200 |
Beyond exam fees, active licensing requires a $5,000 surety bond and $50,000 commercial general liability insurance - budget items that catch a lot of first-time applicants off guard. For a complete line-item walkthrough of every cost involved, read OK-MECH Certification Cost 2026: Complete Pricing Breakdown.
Exam Format: Questions, Timing, and Scoring
The HVACR Contractor Unlimited trade exam is 90 computer-based questions in 240 minutes, requiring a 70% passing score. That works out to roughly two and a half minutes per question if you use the full time - generous compared to many trade exams, but the questions themselves are dense, often referencing code sections, load calculations, or multi-step troubleshooting scenarios rather than simple recall.
One detail that surprises candidates: PSI may embed up to 10 unscored experimental questions into your exam. These are indistinguishable from scored items, and importantly, the time you spend answering them does not count against your 240-minute limit - PSI accounts for this separately. You should never try to guess which questions are experimental; just answer every question as if it counts.
Key Takeaway
Because experimental items don't consume your allotted time, don't panic if the exam "feels longer" than 90 questions should take - the clock is already adjusted for that.
For the exact math behind the 70% threshold and how many questions you can afford to miss, see OK-MECH Passing Score 2026: Exactly What You Need to Pass. And if you're weighing how this exam compares in difficulty to other state trade tests, How Hard Is the OK-MECH Exam? Complete Difficulty Guide 2026 digs into that specifically.
Domain-by-Domain Breakdown (90 Questions)
The trade exam is built from six official subject areas, with a published allocation of 15, 12, 25, 20, 15, and 3 items respectively across the six domains. Air Distribution Systems is confirmed as the largest single domain at 25 of 90 questions - nearly a third of the entire exam.
Domain 1: Electrical Knowledge and Controls (15 items)
Covers control circuits, motor protection, wiring practices, and the electrical side of HVAC/R equipment operation.
- Expect scenario questions tying electrical faults to system symptoms, not just definitions.
Domain 2: Natural Gas (12 items)
Fuel-gas piping, venting, combustion, and appliance installation rules governed by the fuel-gas code.
- Know sizing tables and clearance requirements cold - these are frequently tested with math components.
Domain 3: Air Distribution Systems (25 items - largest domain)
Ductwork design, airflow calculation, balancing, and distribution equipment sizing for unlimited-tonnage commercial systems.
- This is the domain to over-prepare for; it carries nearly 28% of your total score.
- Expect ductulator-based sizing problems.
Domain 4: Refrigeration and Air Conditioning Systems (20 items)
Refrigerant cycles, compressor types, charging, and troubleshooting for large-capacity commercial and industrial systems.
- Given the Unlimited scope, expect questions framed around equipment well above residential tonnage.
Domain 5: Heating Systems (15 items)
Furnaces, boilers, heat exchangers, and combustion safety for commercial-scale heating equipment.
Domain 6: Safety (3 items)
The smallest domain, but tied closely to OSHA reference material you're permitted to bring open-book.
For a deeper dive into each content area with sample topic lists, read OK-MECH Exam Domains 2026: Complete Guide to All 6 Content Areas. It's the natural companion to this study guide.
What You Can Bring: Open-Book References and Rules
This is an open-book exam, but "open-book" doesn't mean unstructured. The permitted references include the specified mechanical and fuel-gas codes, a refrigeration textbook, an OSHA reference, ACCA Manual N, Mathematics for Plumbers and Pipefitters, and an ACCA ductulator. Knowing your references cold - not just owning them - is what separates a fast pass from a candidate who runs out of time flipping pages.
Two mechanical rules matter just as much as which books you bring:
- Pre-highlighting and permanent tabs are allowed - prepare your references in advance.
- Handwritten notes are prohibited. Sticky notes with your own commentary, formulas, or shortcuts will get flagged.
- A PSI-compliant non-programmable calculator is permitted for the math-heavy sizing and load questions.
The current PSI bulletin governing all of this is effective August 31, 2026, so make sure any tabbing or reference prep you do reflects that version rather than an older printout you found online.
A Six-Week Study Timeline Built Around the Domains
Generic study techniques only matter if you point them at the right material in the right order. Here's a domain-weighted schedule that puts your heaviest hours where the exam actually puts its points.
Air Distribution Systems (25 items)
- Work ductulator problems daily until sizing is automatic
- Tab your code book's duct sizing and airflow sections
Refrigeration and Air Conditioning Systems (20 items)
- Focus on commercial-scale refrigerant cycle troubleshooting
- Review Manual N alongside real capacity examples above 25 tons
Electrical Knowledge and Controls & Heating Systems (15 + 15 items)
- Pair these two domains since control logic overlaps both
- Drill motor protection and combustion safety scenarios together
Natural Gas (12 items)
- Master fuel-gas sizing tables and venting clearances
- Confirm which IFGC edition you're using based on your test date
Safety (3 items) plus full-length review
- Quick OSHA reference pass - low point value, low time investment
- Run a full 90-question timed simulation under 240 minutes
Reference organization and final tabbing
- Finalize tabs and pre-highlighting across every allowed reference
- Review weak-domain missed questions from your practice run
Keep a one-page summary of formulas, sizing shortcuts, and code references nearby during this phase - the OK-MECH Cheat Sheet 2026: One-Page Review of Must-Know Facts is built for exactly this kind of final-week consolidation. You can also run timed domain-specific practice sets on the main practice test platform to see which of the six areas still needs work before test day.
Retakes, Business & Law, and Renewal Realities
Passing the trade exam is only half the licensing requirement. You also need to pass the separate Business and Law examination - 50 questions in 120 minutes, also requiring 70% to pass, and also costing $92 per attempt. Both required portions must be passed within three years of your eligibility approval under CIB rules, so don't let one exam linger while you focus entirely on the other.
If you don't pass the trade exam on your first try, the CIB's retake rules are strict on timing:
- 30 days minimum wait after a first failed attempt.
- 90 days minimum wait after any subsequent failed attempt.
Every retake is another $92 fee, which is exactly why first-attempt preparation matters more here than in exams with cheaper or unlimited retakes. If you want a realistic sense of how candidates typically perform and where the exam trips people up, OK-MECH Pass Rate 2026: What the Data Shows covers that in detail.
Once licensed, renewal is annual in your birth month with a $200 contractor renewal fee. Continuing education is light - six approved hours every 36 months - and there's an initial three-year examination exemption after you first pass, meaning you won't need to retest immediately for renewal purposes. For a bigger-picture look at whether the time and cost investment pays off across a career, Is the OK-MECH Certification Worth It? Complete ROI Analysis 2026 and OK-MECH Salary Guide 2026: Complete Earnings Analysis are useful companion reads.
Frequently Asked Questions
90 computer-based questions administered in 240 minutes, with a 70% score required to pass. PSI may also add up to 10 unscored experimental questions that don't count against your time.
Air Distribution Systems, which carries 25 of the 90 questions - the largest of the six official domains, ahead of Refrigeration and Air Conditioning Systems at 20.
No, they're separate exams with separate $92 fees - the trade exam has 90 questions in 240 minutes, while Business and Law has 50 questions in 120 minutes. Both require 70% and must be passed within three years of eligibility approval.
No. Handwritten notes are prohibited, but pre-highlighting and permanent tabs in your approved reference materials are allowed.
You must wait 30 days after a first failed attempt before retaking, and 90 days after any subsequent failure, paying the $92 fee each time.
Passing the HVACR Contractor Unlimited trade exam on your first attempt comes down to respecting how the 90 questions are actually distributed, knowing your open-book references well enough to use them quickly, and treating the registration and fee mechanics as part of your preparation, not an afterthought. Start practicing under real timed conditions on our OK-MECH practice test platform so test day feels like a formality rather than a surprise.