The G3 and G2 exams, in brief
Ontario's gas certificates are issued by the Technical Standards and Safety Authority (TSSA). The G2 builds directly on the G3 — this guide covers both.
- Format
- Multiple choice, four options, one best answer. Written in person at a Prometric test centre. Up to 3.5 hours.
- Pass mark
- 75% — the same for all TSSA Fuels exams.
- Open book
- Hard-copy CSA code book only — unmarked and unaltered, no notes or tabs with writing. Practise with a clean book from day one.
- G3 route
- No prerequisites. Challenge the written exam, then complete a practical skills assessment with a TSSA advisor within one year of passing.
- G2 route
- Valid G3 plus an accredited G3 program or 450 documented hours working as a G3 under proper supervision. Covers units 10–24 on top of G3.
- Retakes
- Three failed attempts on the same exam means completing an accredited training program before writing again.
TSSA does not publish exact question counts or pass rates. Confirm the current exam fee in the TSSA Client Portal when you apply.
What's inside the guide
Built for the open-book exam: every code-check box is a navigation drill you do with your own code book open, because the exam is a code-navigation speed test as much as a knowledge test.
- Getting started — how the G3 and G2 exams work, an 8-week study plan, and exam-day strategy (the three-pass method, time budgeting, reading the last line first)
- Part 1 — Gas Technician 3 (Units 1–9) — safety and WHMIS, tools and fasteners, gas properties and combustion, codes and regulations, electricity basics, manuals and schematics, customer relations, piping and tubing, gas appliances
- Part 2 — Gas Technician 2 (Units 10–24) — advanced piping, controls, building-as-a-system, meters and regulators, conversion burners, water heaters, forced warm air, hydronics, venting practices, air handling
- Quick reference — formula and conversion sheet, the numbers to know cold, and code navigation drills
- Two mock exams — full-length, timed G3 and G2 mock exams with explained answers
Every unit includes learning targets, plain-language core content, Key Point boxes for the facts that show up again and again, Exam Trap boxes for the wrong answers that look right, and a practice quiz with a fully explained answer key.
Built for the current codes
A note on code editions
In June 2026 Ontario moved to the 2025 editions of the B149 series — and clause numbers were renumbered. Most existing practice material online is still keyed to the old codes. This guide is written for CSA B149.1:25 and B149.2:25 with Ontario's 2026 Code Adoption Documents, and its code-check boxes tell you exactly what to verify in your own books before exam day.
Free study resources
Start here, free: our 8-week G3 study plan and G2 exam guide cover exam strategy, code navigation drills, and where candidates lose marks.
Questions
Can I challenge the G3 exam without taking a course?
Yes. An uncertified individual may challenge the TSSA G3 exam with no prerequisites. After passing the written exam, you complete a practical skills assessment arranged with a TSSA Training and Certification Advisor within one year.
What do I need before writing the G2 exam?
A valid G3 certificate, plus either an accredited G3 training program or 450 documented hours working as a G3 under proper supervision. The G2 exam covers curriculum units 10–24 on top of the G3 units — which is why this guide covers both.
Are the exams open book?
Yes. The permitted reference is a hard-copy CSA code book — unmarked and unaltered, with no notes or tabs with writing. Confirm the current rules in the TSSA Certification Examination Preparation Guide before exam day.
What is the pass mark?
75% for all TSSA Fuels exams. After three failed attempts on the same exam, you must complete an accredited training program before writing again.
Which code edition does the guide follow?
The guide is written for CSA B149.1:25 and B149.2:25 as adopted in Ontario by the 2026 Code Adoption Documents (in force June 2026). Because clause numbers changed from the 2020 editions, always verify figures and clause numbers against your own current code books.
Is this an official TSSA study guide?
No. TSSA provides no official study guide or practice exam. This is an independent study aid: not produced, reviewed, or endorsed by the TSSA, CSA Group, Prometric, or any training provider. It doesn't reproduce any examination content and doesn't guarantee a passing grade.
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Walk in ready — for both exams.
All 24 units, 375+ explained practice questions, and two timed mock exams — everything in one PDF, ready to download now.