Based on the Red Seal Plumber standard & the Ontario Building Code (plumbing)
About the certification
In Ontario, Plumber is trade code 306A (not to be confused with 309A, the Construction & Maintenance Electrician). The written Certificate of Qualification (C of Q) exam is administered by Skilled Trades Ontario. Plumber is a Red Seal trade, so Ontario's certifying exam is the interprovincial Red Seal Plumber exam — passing it earns both your C of Q and the Red Seal endorsement.
The Red Seal Plumber exam has 125 multiple-choice questions with a 70% pass mark, and candidates are generally allotted up to about four hours. Questions are built from the Red Seal Occupational Standard for Plumber; day-to-day work in Ontario is governed by the Ontario Building Code (O. Reg. 332/12, Part 7 – Plumbing), which is based on the National Plumbing Code of Canada.
ExamHub's free 306A practice quiz has 128 original questions across seven topic areas that mirror the official exam breakdown, with an explanation for every answer. It is unofficial study practice — always confirm current requirements with Skilled Trades Ontario and the latest code.
What's covered
Categories map to the Red Seal Major Work Activity blocks, with DWV/drainage the most heavily weighted — just as it is on the real exam.
Try a few
Five questions pulled from the full bank, with the answer shown — use the quiz above for the real timed experience.
Why: Trap seals must be at least 38 mm (1½ in.) and not more than 100 mm (4 in.) deep — enough to resist siphonage and evaporation without holding excessive standing water.
Why: Pipe 3 in. (75 mm) and smaller is normally graded at 1/4 in. per foot (about 2%, or 1:50) so solids stay suspended in the flow.
Why: Type K has the thickest wall of the common water tubes, so it is used for buried water service and demanding applications. Type L is typical interior water piping; Type M is thinner still.
Why: An air gap must be at least twice the diameter of the effective supply opening and never less than 25 mm (1 in.) — the physical separation makes back-siphonage impossible.
Why: Residential closed hot-water heating systems commonly use a 30 psi relief valve, matched to the boiler's maximum allowable working pressure to protect against over-pressure.
FAQ
The interprovincial Red Seal Plumber exam has 125 multiple-choice questions. ExamHub's practice bank has 128 original questions, and the timed 'Test Me' mode draws a 100-question practice test.
The Red Seal Plumber exam pass mark is 70%. On the real 125-question exam that's 88 correct; ExamHub uses the same 70% threshold.
Red Seal exams are generally allotted up to about 4 hours. ExamHub's Test Me mode gives you up to 4 hours, which is far more than most people need.
The Red Seal breakdown weights the exam across seven blocks: common occupational skills, preparing and joining pipe, sewers/sewage/DWV systems (the largest block), water service and distribution, fixtures/appliances/water treatment, low-pressure steam and hydronic systems, and specialized systems.
No. These are original questions written by ExamHub from the Red Seal Plumber standard, the National Plumbing Code, and the Ontario Building Code. They cover the same topics but aren't copies of any real exam. Always verify against current code before relying on any value in the field.