Can a make-up air unit cause drafts or cold spots in my Toronto home during winter?

A properly installed and tempered make-up air unit should not cause uncomfortable drafts or cold spots in your Toronto home, but a poorly designed or improperly installed system absolutely can. The key difference is whether the incoming outdoor air is tempered — heated before it enters the living space — and whether the make-up air is delivered to the right location with appropriate diffusion.

During a Toronto winter, outdoor air temperatures regularly drop to -10 to -20 degrees Celsius. A make-up air system that dumps untreated outdoor air directly into your kitchen or living space at those temperatures will create an obvious and miserable cold draft. This is why the Ontario Building Code and good engineering practice require tempering — the make-up air passes through an electric or gas-fired heater before entering the home, warming it to a comfortable temperature. A well-designed tempered make-up air unit heats incoming air to approximately 15 to 18 degrees Celsius before delivery, which is cool enough that you might notice a slight temperature difference near the discharge point but not cold enough to create discomfort. The tempering coil adds to the installation cost, but in Toronto's climate it is absolutely non-negotiable.

The location and method of air delivery matter enormously. Make-up air should ideally be delivered near the range hood or into the kitchen area, since that is where the air is being exhausted from. Some installations deliver make-up air into the return air plenum of the furnace, allowing the furnace blower to mix and distribute it throughout the home. This approach works well because the furnace further tempers the air and distributes it evenly, but it requires the furnace fan to be running whenever the range hood operates. Other installations use a dedicated ceiling or wall diffuser in the kitchen, which should be positioned to avoid blowing directly on cooking or seating areas. A ceiling diffuser that spreads air across a wide area is far better than a small wall grille that creates a concentrated jet of air.

If you are experiencing cold drafts from an existing make-up air system, the most common causes are a failed or undersized tempering element, a thermostat or control issue that is not activating the heater, or a diffuser that is too small and creates a high-velocity air stream. A qualified contractor can diagnose and correct these issues — it may be as simple as replacing a heating element or adjusting the interlocking controls.

One important consideration for older GTA homes — many pre-war and post-war houses in neighbourhoods like the Danforth, East York, and Etobicoke are inherently leaky, with enough natural air infiltration that a make-up air system may introduce less noticeable drafts simply because the home already has significant air exchange. Conversely, modern airtight homes in newer Vaughan, Markham, or Mississauga subdivisions are where make-up air system design is most critical, because these homes have very little natural air leakage to supplement the system. If you need a make-up air system installed or adjusted, Toronto Ductwork can connect you with a local ductwork professional for a free assessment.