A ventilation blockage in Montréal that could have ended in disaster
At AirGreen, we believe every service call tells a story. But some cases go beyond what you’d expect, even for our most experienced technicians. This article recounts one of the most bizarre HVAC ventilation cases we’ve ever encountered in Montréal, where what seemed like a minor airflow issue turned out to be the sign of something much deeper… and more surprising.
The context: recurring complaints in a building in Rosemont–La Petite-Patrie
A property manager reached out to us after receiving multiple complaints from tenants about:
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Persistent foul odors in the hallways.
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Poor indoor air quality in individual units.
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Increased humidity and early signs of mold on some ceilings.
This was a 12-unit multiplex building, equipped with a central ventilation system with heat recovery, installed over ten years ago.
Initial inspection: the system appeared functional… on the surface
Our team began with:
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A mechanical check of the central fan and motor.
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Testing of air intake and exhaust in several units.
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An endoscopic camera inspection of the ductwork.
It was this last step that uncovered the real issue. A compact mass was clogging a main horizontal duct line, cutting off airflow to 5 of the 12 units. The blockage, wedged between two elbows in an inaccessible section, was anything but ordinary.
The surprise: objects found in the ducts (with photos)
Here are a few of the items we removed during the cleaning:
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Three tennis balls (likely dropped in through an open rooftop grille).
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A sock stuck in a damper flap.
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A melted plastic bag, probably sucked in during roof work.
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Pieces of rigid foam insulation from nearby renovations.
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Several food wrappers and pieces of cardboard.
Conclusion: these items created a complete blockage, reducing HVAC system efficiency by more than 50% in affected areas.
Consequences on the HVAC system and residents’ health
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Backflow of stale air into several units.
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Microbial contamination worsened by stagnant moisture inside the ducts.
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Motor overload caused by abnormally high static pressure.
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Odor transfer between apartments.
AirGreen’s intervention: deep cleaning and a lasting solution
Here’s what we did:
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Targeted opening of affected ducts using specialized tools.
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High-pressure industrial vacuuming to remove all debris.
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Full antibacterial cleaning with a biodegradable enzymatic solution.
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Installation of protective grilles on exterior openings.
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Set up of an annual HVAC maintenance program.
Result: within 48 hours, air quality was fully restored and complaints disappeared. The property manager decided to roll out the same process across his other buildings in Montréal.
Why this kind of situation is more common than you think
At AirGreen, we regularly see blockages caused by a lack of preventive maintenance:
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Birds and small animals often sneak in through damaged or open vents.
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Poorly shielded renovation work leads to debris infiltrating the HVAC system.
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Household items falling into vents are never retrieved or reported.
Our recommendations for Montréal and its boroughs
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Annual visual inspections of main duct lines, even if the system seems fine.
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Regular HVAC maintenance to prevent dust, mold, and foreign object buildup.
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Use of wire mesh intrusion guards on ventilation outlets.
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Educating occupants about the proper and safe use of air vents.
AirGreen: unmatched field expertise in HVAC maintenance in Montréal
Whether it’s a residential multiplex, a commercial building, or a condo complex, we tailor every intervention to the real conditions on the ground in Montréal. Our technicians are trained to quickly detect obstructions, deliver real solutions, and prevent major ventilation failures.
We service all of Montréal’s boroughs, including Le Plateau-Mont-Royal, Rosemont–La Petite-Patrie, Mercier–Hochelaga-Maisonneuve, Côte-des-Neiges, Ahuntsic, and Villeray.
Managing a building in Montréal and noticing signs of ventilation issues? Call AirGreen for a full inspection, with real photos and long-term solutions.