Why does my Toronto condo hallway pressurization system affect my unit ventilation?

Your Toronto condo's hallway pressurization system is designed to be your primary source of fresh air — the building pumps conditioned outdoor air into the corridors at positive pressure, and that air enters your suite through the gap under your entry door, driven by the negative pressure created by your bathroom and kitchen exhaust fans. When this system is not working properly, or when building physics work against it, your unit ventilation suffers in ways that feel mysterious but have clear explanations.

The corridor pressurization model was the standard ventilation approach for Toronto high-rise condos for decades, and the vast majority of buildings across the downtown core, Yonge corridor, North York, and Scarborough still use it. The concept is simple: a rooftop makeup air unit (MAU) draws in outdoor air, heats or cools it to a comfortable temperature, and distributes it through ductwork to each floor's corridor. The corridor is maintained at a slightly higher pressure than individual suites, so air naturally flows from the hallway into your unit under the entry door. Your bathroom exhaust fan (connected to a shared vertical exhaust riser) pulls air through the suite and exhausts it to the roof, completing the ventilation cycle.

The problem is that this system rarely works as designed in real-world Toronto conditions. Research by CMHC and building science experts has consistently shown that corridor pressurization delivers far less fresh air to individual suites than intended. Several factors undermine the system in Toronto's climate.

Stack effect is the biggest disruptor. In winter, warm air inside the building rises through elevator shafts, stairwells, garbage chutes, and any other vertical openings. This creates positive pressure on upper floors and negative pressure on lower floors. On lower floors (roughly the bottom third of the building), cold outdoor air gets pulled in through every crack and gap in the building envelope — under exterior doors, through parking garage connections, and around window frames. These lower-floor units often feel drafty and cold in winter, not because their windows leak but because stack effect is pulling massive amounts of cold air through the building. Upper-floor units experience the opposite — air is being pushed out through the building envelope, and the corridor pressurization cannot overcome this outward pressure. Upper-floor residents get almost no fresh corridor air and often complain about stale air, cooking odours from other units travelling up through the exhaust riser or vertical shafts, and condensation on windows from trapped moisture.

Wind loading compounds the problem. Toronto's waterfront location and the canyon effect of downtown streets create significant wind pressures on building faces. The windward side of your building experiences positive pressure (air being pushed in), while the leeward side experiences negative pressure (air being sucked out). If your unit is on the leeward side during a strong west wind, the wind is pulling air out of your unit faster than the corridor system can replace it, potentially causing your bathroom exhaust to backdraft — pulling air from the exhaust riser back into your bathroom, bringing odours from neighbouring units with it.

What you can do as a unit owner: Ensure your entry door undercut is not sealed — that gap is designed to allow corridor air into your suite. Make sure your bathroom exhaust fan is working properly and running when needed. If you experience persistent odour transfer from neighbours, install a spring-loaded backdraft damper on your bathroom exhaust branch duct ($15 to $40). For a long-term solution, consider an in-suite ERV unit that provides dedicated fresh air independently of the corridor system — these cost $1,500 to $4,000 installed and give you control over your own ventilation. Report building system problems (weak corridor air, non-functioning exhaust, odour transfer) to your property manager — the rooftop MAU and exhaust fans require regular maintenance to function properly. Find ventilation professionals through the Toronto Construction Network at torontoconstructionnetwork.com.