In a forced-air heating system, supply vents deliver conditioned air to rooms, while return vents draw air back to the furnace for recirculation. Their placement affects both air distribution and comfort.
For Ontario homes, distinguish the requirements of OBC Section 9.33 from design guidance in the HRAI Residential Air System Design Manual.
Supply air outlets
A warm-air supply outlet is required in every finished room adjacent to unheated space. This includes more than rooms with exterior walls: a room above an unheated garage can also qualify.
Where the room has an exterior wall, the outlet generally must direct warm air across at least one exterior wall or window. Placement near a window can help offset cold surfaces and downdrafts. The code allows exceptions where this is impractical in bathrooms, utility rooms and kitchens, and permits certain purpose-designed high-wall or ceiling diffusers. Unfinished basements also require supply outlets—at least one for every 40 m² of floor area. Ontario Building Code, Article 9.33.6.11
Furniture placement matters, too. Keep outlets clear and consider where the air will blow, particularly around beds and seating.
Return air inlets
At least one return inlet is required on each floor level. An exception applies where a level is less than 900 mm above or below an adjacent level that already has a return inlet. The 1,100 mm figure in your draft should therefore be corrected.
Every room also needs a path for air to return, which may use a ducted return, a suitable gap beneath a door or a louvred door. Return inlets must not be installed in an enclosed room or crawl space that supplies combustion air to a furnace. Ontario Building Code, Article 9.33.6.12
A central return can be a practical design choice, but its location and capacity should account for the layout and airflow from individual rooms.
