Ontario 306A Plumber Exam: How It Works and How to Prepare

Who runs the exam

Certification for Ontario's skilled trades is managed by Skilled Trades Ontario. They handle eligibility, exam booking and the current exam format, so check their website for the latest details before you book.

Plumber is also a Red Seal trade, so the exam covers knowledge used across Canada, while Ontario work itself is governed by the Ontario Building Code.

Pass mark

The pass mark for Ontario certification exams is 70%. Treat 70% as the floor: aim to score well above it on practice exams before the real thing.

What's on it

Expect multiple-choice questions on code, drainage and venting, water distribution, pipe sizing, fixtures, installation practice, safety, trade math and related systems such as hydronic heating. The weighting follows the trade's published exam breakdown.

A 6-week study plan

Week 1: take a full diagnostic test to find your weak areas.

Weeks 2–4: study one or two weak subjects at a time, with short practice quizzes and the code book open.

Week 5: take timed, full-length practice exams to build pace.

Week 6: review every missed question, revisit the code tables you struggled with, and rest the day before.

On exam day

Read every question twice, flag hard ones and come back, and don't leave anything blank. Manage your clock so you have time to review your flagged questions.