Why is one room in my Toronto home always hotter or colder than the rest?

A single room that is consistently too hot or too cold almost always points to a ductwork issue — either insufficient supply air reaching the room, inadequate return air leaving it, or a combination of both. This is an extremely common problem in GTA homes, particularly in post-war and 1970s-1990s construction where duct systems were designed for heating only and air conditioning was added later.

The most likely culprit is a supply duct that is undersized, too long, or has too many bends. Every room in your home needs a specific volume of conditioned air (measured in CFM) to maintain comfortable temperatures, and that volume depends on the room's size, window area, insulation quality, and sun exposure. If the duct serving the problem room is a 5-inch flex duct with two 90-degree turns and a 25-foot run, it simply cannot deliver enough air. Each 90-degree bend adds resistance equivalent to 10 to 15 feet of straight duct, so a run with multiple bends effectively behaves like a duct twice its actual length. A contractor can measure airflow at the register with a flow hood — if the room needs 80 CFM and the register is only delivering 40, you have found the problem.

In many older Toronto homes, flex duct serving the problem room may be crushed, kinked, or disconnected. Flex duct in attic spaces across Mississauga, Brampton, and Vaughan frequently sags between support points, creating dips that restrict airflow. In basements, flex duct routed around obstacles sometimes gets kinked at sharp angles, cutting airflow by 50 percent or more. A visual inspection of the duct run — if accessible — can reveal these issues.

Missing or blocked return air is the other common cause. If the problem room has a supply register but no return air grille, the room builds positive pressure as conditioned air is pushed in with no easy exit path. This pressure resists additional supply air, making the room underserved. The gap under the door provides some return air path, but it is rarely sufficient, especially if the door is closed at night. Adding a return air duct to the room typically costs $300 to $800 and can solve the problem entirely.

Sun exposure and insulation also play major roles. South and west-facing rooms in Toronto absorb significantly more solar heat in summer, especially rooms with large or poorly insulated windows. A room over an uninsulated garage or above a cantilevered bay window will always be harder to condition because of heat loss through the floor. In these cases, the ductwork may actually be adequate, but the room's heating and cooling load is higher than what the duct system was designed to handle.

Before spending money on duct modifications, try some no-cost adjustments first. Open the register damper in the problem room fully, and partially close registers in rooms that are already comfortable — this redirects some airflow to where it is needed. Make sure furniture is not blocking the supply register or return grille. If these basic adjustments do not help, a professional airflow assessment is worth the investment. Get matched with a ductwork contractor for a free estimate through Toronto Ductwork.