What the 306A exam is
Plumber (trade code 306A) is a compulsory trade in Ontario under the Building Opportunities in the Skilled Trades Act, 2021. To work in the trade legally you must hold a Registered Training Agreement, a Provisional Certificate of Qualification or a Certificate of Qualification (C of Q), and appear on the Skilled Trades Ontario Public Register. The apprenticeship is set at 9,000 hours: 8,280 hours on the job and 720 hours of in-school training over three levels.
When you finish your apprenticeship, or are approved through a Trade Equivalency Assessment, you write the certifying exam. Passing it leads to your C of Q from Skilled Trades Ontario. In Ontario the trade is part of the Interprovincial Red Seal Program, and the Red Seal Plumber exam is the national standard for the trade.
| Part of the exam | What to expect |
|---|---|
| Questions | 125 multiple-choice questions on the Red Seal Plumber exam, each worth one mark |
| Options | Four choices, exactly one correct, with no trick questions |
| Writing time | Four hours |
| Pass mark | 70% |
| Supplied at the exam | A formula sheet, an acronym list, a calculator if needed, and code book information where required |
| Language | English or French in Ontario |
| If you do not pass | In Ontario, a 30-day waiting period before you can rewrite, and the exam fee is paid again |
The Red Seal program says that for this trade about 15 to 25% of questions test knowledge and recall, 60 to 70% test procedures and application, and 10 to 20% test critical thinking, such as working through a calculation or diagnosing a fault. Four hours for 125 questions gives you just under two minutes a question. Always check your Authorization to Test letter for the details of your own sitting.
How the exam is weighted
Red Seal exam questions come from the Red Seal Occupational Standard for the trade. The official exam breakdown gives each major work activity a set number of questions. Our seven sections follow the same activities, and our 125-question mock exams use the same weighting.
| Major work activity | Red Seal questions | What it covers |
|---|---|---|
| A. Common occupational skills | 14 | Safety, lockout, ladders and trenches, tools, layout and offsets, documentation |
| B. Tube, tubing and pipe | 13 | Cutting, bending, joining and supporting copper, plastic, steel and cast iron, thermal expansion |
| C. Sewers, sewage treatment and DWV | 32 | Building sewers, septic systems, traps, venting, slope, sizing by fixture units, cleanouts, testing |
| D. Water service and distribution | 24 | Water service, pressure and sizing, backflow prevention, cross-connection control, private water pressure systems |
| E. Fixtures, appliances and water treatment | 17 | Fixture installation, water heaters and relief valves, softeners, filters, UV and RO |
| F. Hydronic systems | 16 | Hydronic piping and components, heating and cooling equipment, flow and heat calculations |
| G. Specialized systems | 9 | Process piping, medical gas, compressed air, rainwater and other non-potable systems |
Low-pressure steam and potable water fire protection systems are not common core, so the Red Seal exam asks no questions on them.
Calculations you should be fast at
The formula sheet you get on exam day lists the formulas and constants, but it does not tell you which one to use. Practise until these feel automatic, and always carry your units through:
- Pressure and head. 9.81 kPa for every metre of water, or 0.433 psi per foot, both ways.
- Slope and offsets. Grade as drop over run (1 in 50 is 2%), and travel = set x 1.414 for a 45 degree offset.
- Pipe volume, flow and force. Area of a circle, volume of a cylinder, flow = area x velocity, and force = pressure x area on a test cap.
- Thermal expansion. Length x temperature difference x the coefficient for the pipe material.
- Hydronics. Btuh = gpm x 500 x temperature difference, 12 000 BTU to a ton, and 240 Btuh per square foot of EDR.
- Water treatment. Grains per gallon to ppm, and softener capacity in grains.
The code questions
The Red Seal exam is based on the national code book, and the questions will not always tell you that they are code questions. In Ontario, plumbing is now built to the 2024 Ontario Building Code (O. Reg. 163/24), which replaced the 2012 code on January 1, 2025. Exam candidates use the code information supplied at the exam, so our questions do not ask you to memorize code tables or article numbers. They test the principles behind the rules, such as why drains need slope, how traps lose their seal and how backflow happens, and the calculations you will do with the code data in front of you.
How to prepare
Start with the official Red Seal self-assessment and the exam breakdown to find your weaker areas. Use the occupational standard, not only your college notes, because the exam covers the full scope of the trade across Canada. Then drill one section at a time here, read every explanation, and finish with full timed mocks of 125 questions in four hours. Aim to score well above 70% in practice so a few hard questions on the day do not sink you.
Aptitude Tests Canada is an independent practice platform. We are not affiliated with or endorsed by Skilled Trades Ontario, the Red Seal Program or the Government of Ontario. Our questions are original practice questions, not real exam questions, and they do not reproduce the National Plumbing Code.
Three worked examples
One question from different sections of the full pack, with the answer and explanation.
An extension ladder 6 m long is used without being fastened at the top. Under O. Reg. 213/91, how far should its base be from a point directly below the top of the ladder?
- Between 0.6 m and 1.2 m
- Between 2.0 m and 3.0 m
- Between 1.5 m and 2.0 m
- At least 3.0 m
Which copper tube is meant to be bent on site with a tube bender?
- Soft (annealed) temper Type K or L
- Hard drawn Type M water tube
- Hard drawn DWV copper
- Any copper, if it is heated red hot first
A 2 in. drain runs 20 ft at a slope of 1/4 in. per foot. How much does it fall over the run?
- 2.5 in.
- 10 in.
- 5 in.
- 1.25 in.