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OBC DIVISION B · PART 6 — HEATING, VENTILATING AND AIR-CONDITIONING

Where can exhaust ducts and vents discharge in Ontario?

Exhaust ducts must discharge directly outdoors, located so exhaust air cannot re-enter the building through air intakes, windows or doors, and so it does not create a hazard or nuisance.

Code reference — verbatim
Exhaust ducts and outlets shall discharge directly to the outdoors, and outdoor exhaust openings shall be located so that the exhaust air will not create a hazard, contaminate air intakes or re-enter the building.
OBC Division B, Section 6.2 (and 9.32./9.33. for houses)
What this means in practice

The recurring code intent is separation of dirty air from clean air: exhaust outlets must keep clearance from outdoor air intakes, operable windows and doors, and property lines, with distances depending on the contaminant and system. Bathroom and kitchen exhausts cannot terminate in attics, soffit cavities that feed attic vents, or crawl spaces — a chronic deficiency that causes attic mould. Clothes dryer ducts have additional rules: smooth-wall duct, sealed joints (no screws projecting into the airstream), length limits per the manufacturer, and no screening at the termination that would trap lint. Combustion appliance venting is regulated separately under the fuel codes (CSA B149.1, TSSA), not the OBC.

Plain language

Whatever you blow out of the building — steam, smells, dryer lint — has to actually leave the building and stay out. Venting a bathroom fan into the attic is one of the most common and most damaging mistakes in home renovations.

Related questions

What are the ventilation requirements for buildings in Ontario?Is an HRV required in new homes in Ontario?

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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.