The Ontario Building Code | Make-up Air
6.2.3.11. Make-up Air
(1) In ventilating systems that exhaust air to the outdoorref ="http://thehandyforce.com/doors/" title ="Toronto Door installer">doors, provision shall be made for the admission of a supply of make-up air in sufficient quantity so that the operation of the exhaust system and other exhaust equipment or combustion equipment is not adversely affected.
(2) Make-up air facilities required by Sentence (1) shall be interlocked with the exhaust devices they serve so that both operate together.
(3) Where make-up air facilities are intended to introduce air directly from the outdoorref ="http://thehandyforce.com/doors/" title ="Toronto Door installer">doors to occupied parts of the building in winter, they shall incorporate means of tempering that air to maintain the indoor design temperature.
In Plain Language
Ventilating systems that exhaust air outdoors must provide for a sufficient supply of make-up air, so the exhaust system doesn't depressurize the building or interfere with combustion appliances and other exhaust systems.
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.