G2 vs G3 at a glance
The biggest mistake G2 candidates make is treating the exam like a G3 refresher. The G3 material is still tested — but the new units are where the exam decides your grade.
- G3 eligibility
- No prerequisites. Any uncertified individual may challenge the written exam.
- G2 eligibility
- A valid G3 certificate plus an accredited G3 training program or 450 documented hours working as a G3 under proper supervision.
- G3 curriculum
- Units 1–9: safety, tools, gas properties and combustion, codes, electricity basics, manuals, customer relations, piping, appliances.
- G2 curriculum
- Units 1–9 plus units 10–24: the advanced systems listed below.
- Format & pass mark
- Multiple choice at a Prometric test centre, hard-copy unmarked code book permitted. 75% to pass — same as G3.
- Retake rule
- Three failed attempts on the same exam means completing an accredited training program before rewriting. This applies to the G2 too.
What units 10–24 actually add
The G2 units move from individual appliances to whole systems — and from installing to diagnosing.
- Advanced piping practices — larger and more complex piping layouts, sizing for bigger loads.
- Controls — how gas controls work and fail. Candidates consistently rate this the hardest unit.
- Building as a system — how the building envelope, ventilation, and combustion air interact.
- Meters and regulators — selection, installation, and pressure regulation.
- Conversion burners — converting appliances between fuels, with the code rules that govern it.
- Water heaters — types, sizing, venting, and installation requirements.
- Forced warm air systems — furnaces, ducting, and airflow fundamentals.
- Hydronics — boilers and hot-water heating systems; calculation-heavy, so practise with numbers.
- Venting practices — vent sizing and configurations. A classic exam-trap zone.
- Air handling — combustion air, dilution air, and ventilation requirements.
Our G3 & G2 study guide covers all fifteen of these units with the same treatment as the G3 material: Key Point boxes, Exam Trap boxes, code-check drills, and a practice quiz with explained answers for every unit.
Study strategy: it depends on your G3
If your G3 is fresh (within the last year or two), you don't need to re-study units 1–9 from scratch. Skim them for the numbers and rules, then spend the bulk of your time on units 10–24. A diagnostic quiz on the G3 units will tell you where the rust is.
If it's been several years, be honest with yourself: the G3 foundation is fair game on the G2, and field experience doesn't automatically preserve exam knowledge. Budget time to re-cover units 3 and 4 (gas properties, codes) and unit 8 (piping), because the G2 units assume them.
Either way, the 450 supervised hours or accredited program behind you is an advantage the exam can't see — convert it into marks by connecting every new concept to something you've actually touched in the field. Exam questions on controls and hydronics read very differently once you've troubleshot them for real.
The units that trip people up
Three areas account for a disproportionate share of G2 failures:
- Controls. Not memorization material — you need to reason about what happens when a control fails or a sequence is interrupted. Draw the logic out on paper until the sequences feel obvious.
- Hydronics. Calculation-heavy. Work practice problems with a calculator, and keep your unit conversions disciplined: imperial/metric mix-ups are the cheapest marks to lose.
- Venting and air handling. The code rules here are detailed and scenario-driven, which makes them perfect exam fodder. These are pure code-navigation questions — practise finding the right clause fast, with your own clean code book, exactly as you'd do in the exam.
Code editions matter more at G2
Ontario adopted CSA B149.1:25 and B149.2:25 in June 2026, and clause numbers were renumbered versus the 2020 editions. At G2 level, where so many questions are clause lookups, training your navigation on the old numbering is actively harmful. Study from material written for the 2025 editions and verify every figure against your own current code books. Our guide is written for B149.1:25 / B149.2:25 throughout.
Exam day: same exam, more ground to cover
The G2 is the same format as the G3 — multiple choice, open book, 75% to pass, written at Prometric — but with fifteen more units behind it, pacing matters even more. Use the three-pass method: answer everything you know cold first without opening the book, then work the questions that need a code lookup or calculation, then wrestle with the hard ones. Read the last line of each question first, answer every question (an unanswered one can never earn a mark), and don't leave a question you've half-solved — elimination plus educated guessing beats a blank.
And respect the retake rule: three failed attempts on the G2 means completing an accredited training program before you can write again. That's an expensive reset. Two honest, timed mock exams before you book — scored at 80% or better, not just 75% — are the cheapest insurance you can buy.
Questions
What do I need before I can write 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.
Does the G2 exam cover the G3 material too?
Yes. The G2 builds directly on the G3: it covers curriculum units 10–24 on top of the G3 units 1–9. That's why a single guide covering all 24 units is the efficient way to prepare.
What is the G2 pass mark?
75%, the same as all TSSA Fuels exams. After three failed attempts on the same exam you must complete an accredited training program before rewriting.
Is the G2 exam open book?
Yes. The permitted reference is a hard-copy, unmarked and unaltered CSA code book. Confirm the current rules in the TSSA Certification Examination Preparation Guide before exam day.
One guide, all 24 units.
Our 133-page G2 & G3 guide covers units 1–24 with 375+ explained practice questions, code navigation drills, and two full-length timed mock exams — written for B149.1:25 and B149.2:25.