The Ontario Building Code | Protection Against Depressurization
9.32.3.8. Protection Against Depressurization
(1) When determining the need to provide protection against depressurization, consideration must be given to,
(a) whether the presence of soil gas is deemed to be a problem, and
(b) the presence of solid fuel-fired combustion appliances.
(2) Where a solid fuel-fired combustion appliance is installed, the ventilation system shall include a heat recovery ventilator that is designed to operate so that the flow of exhaust air does not exceed the flow of intake air in any operating mode, and that complies with the requirements of Article 9.32.3.11.
(3) The provision of make-up air is not required for mechanical exhausting devices operating a subfloor depressurization system installed for the purpose of reducing the risk of radon ingress.
In Plain Language
The ventilation system must include protection against depressurization, as set out in this article, since a mechanical system that extracts more air than it supplies can cause backdrafting of combustion appliances.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.