Make-Up Air Systems

Make-up air systems solve a problem that most GTA homeowners do not know they have until something goes wrong — and when it goes wrong with combustion appliances, the consequences can be deadly. Every cubic foot of air exhausted from a home by range hoods, bathroom fans, dryer vents, and fireplaces must be replaced by air entering from somewhere. In older, leaky Toronto homes, replacement air infiltrates through gaps in the building envelope — around windows, doors, and through the hundreds of small penetrations that characterize pre-1990 construction. But the newer, tighter homes being built across the GTA in Milton, Vaughan, Brampton, and Whitby are sealed so effectively that powerful exhaust appliances can depressurize the home faster than air can leak in, creating negative pressure that backdrafts gas furnaces, water heaters, and fireplaces. Backdrafting pulls combustion gases — including carbon monoxide — into the living space instead of sending them up the flue. Ontario Building Code addresses this directly: when total exhaust capacity in a dwelling exceeds 75 litres per second (approximately 160 CFM), a make-up air system must be provided to replace the exhausted air. In practice, this threshold is easily exceeded by a single high-performance range hood, which is why make-up air installation has become a standard part of kitchen renovation projects in newer GTA homes. The most common make-up air solutions are motorized dampers that open when the range hood activates, drawing outdoor air through a dedicated duct with an inline heater that tempers the incoming air in winter. More sophisticated systems use energy recovery ventilators (ERVs) or heat recovery ventilators (HRVs) to transfer heat from outgoing exhaust air to incoming make-up air, reducing the energy penalty of bringing cold outdoor air into a heated home. Integrating make-up air with the existing HVAC system requires careful engineering. The incoming air must be distributed without creating uncomfortable cold drafts, and the system must be balanced so that the home operates at neutral or slightly positive pressure when exhaust appliances are running. In the GTA's climate, where outdoor temperatures drop to minus 20 degrees Celsius or lower in January and February, an untempered make-up air system that dumps raw outdoor air into the home is impractical — the air must be heated before it reaches the occupied space, and the heating capacity must be sized to handle the worst-case winter scenario. Typical make-up air system installation in GTA homes costs $2,000 to $5,000 depending on whether a simple motorized damper or a full ERV/HRV integration is required.

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