How must heating and cooling systems be sized for houses in Ontario?
Equipment capacity must be based on a room-by-room heat loss and heat gain calculation, performed in accordance with CSA F280 or equivalent good practice, rather than rules of thumb, so the system matches the specific house at local design temperatures.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
The CSA F280 calculation is the residential equivalent of Manual J and is what building departments and TSSA-licensed contractors should produce with permit drawings. Rule-of-thumb sizing by floor area routinely oversizes furnaces in modern airtight, well-insulated homes, causing short-cycling, comfort complaints and, for air conditioners, poor dehumidification. Oversizing matters even more for cold-climate heat pumps, where balance-point selection drives both comfort and operating cost. Insist on the room-by-room output, since it also determines duct and register sizing, not just the appliance nameplate.
Contractors cannot just guess furnace size by square footage. The code requires a proper heat-loss calculation for your actual house, its insulation, windows and location, so the equipment is neither wheezing undersized nor wastefully oversized.
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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.