Uneven indoor air quality: the invisible issue behind Montréal’s smog
While smog is becoming an increasingly pressing public health issue across Greater Montréal, one key reality is often overlooked: not all buildings are equally protected from pollution. Some offer remarkable defense against fine particles, allergens, and outdoor pollutants, while others let in stale air with no resistance. Why such a stark difference? At AirGreen, we conducted a comparative study on mechanical ventilation across various residential and commercial buildings in Montréal, Laval, Longueuil, the South Shore, and the North Shore. Here's what we found.
Smog in Montréal: a recurring threat
Understanding the phenomenon
Smog is a harmful mix of fog and pollutants, including fine particulate matter (PM2.5), ground-level ozone, and nitrogen oxides. It’s often intensified by summer heat, heavy traffic, and industrial activity.
Health risks
Prolonged exposure to smog can lead to respiratory problems, eye irritation, headaches, and, over time, worsen cardiovascular or lung diseases. Children, seniors, and people with asthma are particularly vulnerable.
Comparative study: AirGreen’s field results
Methodology
We compared 15 buildings in different areas: six in Montréal (Plateau, Rosemont, Villeray), three in Laval, two in Longueuil, two on the South Shore (Boucherville, Saint-Hubert), and two on the North Shore (Blainville, Terrebonne). Our criteria included ventilation system efficiency, air renewal rate, particulate filtration, and HVAC maintenance levels.
High-performance vs underperforming systems
Our results showed a direct correlation between indoor air quality and the type of HVAC system installed:
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Buildings equipped with certified HVI heat recovery ventilators, like Venmar or Lifebreath ERV/HRV models, had indoor fine particle levels 60 to 70% lower than those with outdated or poorly maintained systems.
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Buildings using a HEPA filter combined with a central heat pump system (e.g., MIDEA EVOX G3 or Bosch BOVA R-454B) showed significantly better filtration—even during high-pollution days.
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On the other hand, buildings using basic exhaust fans or partially open windows often had worse indoor air quality than outdoor levels.
Case study: comparing two similar buildings
Building A – Rosemont (Montréal)
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Year built: 1985
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HVAC system: natural ventilation + wall-mounted air conditioner
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Issues: smog infiltration, poor air circulation, mold
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Result: indoor PM2.5 level above 85 µg/m³ during smog alerts
Building B – Plateau Mont-Royal (Montréal)
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Year built: 1982 (renovated in 2023)
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HVAC system: mechanical double-flow ventilation with MERV 13 filter + central Fujitsu KZAH heat pump
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Result: indoor PM2.5 level stable at 15 µg/m³, even during high smog alerts
Why do some buildings “breathe” better than others?
The importance of HVAC design
Well-designed buildings incorporate controlled airflow, avoiding pressure imbalances that pull in outdoor pollutants. Properly insulated ductwork, balanced registers, and CO2 sensors help regulate flow in real time.
The critical role of HVAC maintenance
Even the best systems lose their effectiveness without regular maintenance. We identified many clogged filters, dirty exchangers, or failing motors in systems over 10 years old.
AirGreen in action: how we help buildings breathe better
Complete audit and diagnostics
At AirGreen, we always start with a ventilation audit: duct inspections, airflow analysis, indoor air quality testing (CO2, PM2.5, relative humidity), and thermography if needed.
Tailored recommendations
Based on our findings, we offer custom solutions:
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Installation of cold-climate certified heat recovery ventilators (HRVs)
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Replacement of outdated HVAC systems with energy-efficient heat pumps with integrated ventilation
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Upgrading filters (MERV 13 to HEPA)
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Ongoing maintenance through AirGreen service contracts
Examples of successful interventions
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Longueuil – High school: installation of a mechanical ventilation system with Bosch IDS Premium heat pump + CO2 sensors. Result: 65% drop in CO2 during peak hours.
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Blainville – Office building: replaced 10 individual units with a centralized system with heat recovery. Result: higher energy efficiency and improved comfort during smog alerts.
Key takeaways for building managers
Inadequate ventilation is a serious risk
A building without a proper air filtration or renewal system is a hazardous environment—not just for occupants’ health, but also for the equipment itself (clogging, condensation, duct corrosion).
Investing in quality ventilation pays off
A well-designed system reduces sick days, improves occupant comfort, extends HVAC equipment lifespan, and lowers heating and cooling costs.
Turn to AirGreen
With our recognized HVAC expertise across Montréal, Laval, Longueuil, the North Shore, and the South Shore, we offer modern, durable, and climate-adapted technical solutions that meet today’s environmental challenges.