OBC 9.32.3.7 & 9.32.3.8: Expert Guide to Supplemental Exhaust and Depressurization in Ontario
Sarah's Expert Insight
OBC Compliance Specialist
"At empcontracting.ca Inc. your construction contractor in London, Ontario, we prioritize these ventilation standards to prevent backdrafting in airtight modern homes. Whether we are retrofitting an Oakville estate or building a new cottage in Muskoka, ensuring your kitchen exhaust is balanced with tempered makeup air is a non-negotiable safety requirement for protecting your family from combustion gases."
Understanding the 2024 Ontario Building Code (OBC) is critical for ensuring air quality and safety in residential construction. Sections 9.32.3.7 and 9.32.3.8 outline specific requirements for supplemental exhaust fans and the mechanical balance required to prevent dangerous depressurization.
Section 9.32.3.7: Supplemental Exhaust Requirements
Kitchen and Bathroom Capacity Standards
According to the code, most kitchens must be equipped with a supplemental exhaust fan providing a rated capacity of at least 50 L/s. However, exemptions apply if the principal ventilation fan draws directly from the kitchen and can be toggled to a high-exhaust rate (at least 2.5 times the minimum capacity) via a manual switch labeled “KITCHEN EXHAUST.”
Installation and Manual Controls
For bathrooms or water-closet rooms lacking a principal ventilation intake, a supplemental fan with a minimum capacity of 25 L/s is required. All supplemental fans must feature a manual switch within the room they serve. If automatic controls like dehumidistats are used, the manual switch must still be able to override the system to activate the fan at any time.
Section 9.32.3.8: Protection Against Depressurization
Makeup Air Requirements
In homes containing fuel-fired heating appliances that are not direct-vented, the OBC mandates protection against depressurization. When high-capacity exhaust devices are active, a makeup air fan must deliver outdoor air at a rate equal to (or up to 10% greater than) the exhaust capacity to maintain pressure balance.
Temperature and Air Distribution
To maintain occupant comfort and system integrity, makeup air must be introduced to unoccupied areas or tempered to at least 12°C before being distributed into occupied areas of the home. This ensures that ventilation does not compromise the home's thermal performance or safety.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.