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

What are the ventilation requirements for buildings in Ontario?

Part 6 requires buildings to be ventilated by natural or mechanical means, with mechanical ventilation systems designed, constructed and installed to the rates and methods of ASHRAE 62.1.

Code reference — verbatim
Every building shall be ventilated by natural or mechanical means, and mechanical ventilation systems shall be designed, constructed and installed in conformance with good engineering practice as described in the ASHRAE Handbooks and ANSI/ASHRAE 62.1, 'Ventilation for Acceptable Indoor Air Quality'.
OBC Division B, Section 6.2 (Ventilation)
What this means in practice

For Part 3 buildings, the practical requirement is an engineered ventilation design delivering the outdoor air rates of ASHRAE 62.1, which vary by occupancy — offices, classrooms, gyms and restaurants each have their own people-based and area-based rates. During occupied hours the system must maintain those rates, and exhaust-dominant spaces (washrooms, kitchens, parking garages) have dedicated exhaust requirements. Houses and small residential buildings instead follow Section 9.32, which prescribes a principal ventilation fan (typically an HRV in Ontario new construction due to energy efficiency requirements) sized by bedroom count. HVAC drawings for permit must show the ventilation rate calculations.

Plain language

Every building needs a steady supply of fresh outdoor air, sized to how many people use the space and what happens in it. Big buildings get an engineered system; houses get a fresh-air fan — usually an HRV — sized by the number of bedrooms.

Related questions

Where can exhaust ducts and vents discharge 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.