By the Ventilation Vortex Air team—specialists in indoor air quality in Montreal
The summer of 2025 was brutal. Wildfires pushed Montreal’s IQA as high as 131; on some days, you could barely see Mount Royal from the Plateau. And yet, many families believed they were safe at home, with their windows closed and the air conditioner running.
The reality is that indoor air can be 2 to 5 times more polluted than outdoor air, especially in winter when homes are tightly sealed. This isn’t just a made-up number—it’s backed by data from the Air Quality Monitoring Network (RSQA) and studies by Environment Canada.
So yes, Montreal’s air quality index does indeed affect your homes. But how? And more importantly, what can we do about it?
Understanding the Air Quality Index (AQI) in Montreal
The IQA is the tool used in Quebec to measure air pollution on a daily basis. It takes into account fine particulate matter (PM2.5), ozone, nitrogen dioxide, and other contaminants present in the air we breathe outdoors.
The RSQA, managed by the City of Montreal, publishes this data in real time for the various boroughs. But what few people know is that these figures have a direct impact on what happens inside your home.
What does an IQA of 41… or 131 mean?
In 2026, the average AQI in Montreal is around 41, which represents an increase of 37 % compared to previous years. This is considered »acceptable,» but it remains a cause for concern.
During the episodes of smog caused by wildfires in July 2025, the AQI rose to between 131 and 164. At this level, vulnerable individuals—including children, seniors, and people with asthma—begin to feel the effects within just a few hours. Children, in particular, are 30 % more affected than adults in these situations.
And on 70 % days during the summer of 2025, levels were recorded that affected indoor air quality. This isn’t an exceptional summer—it’s the new normal.
Difference Between the IQA and the Air Quality Health Index (AQHI)
The IQA is used primarily in Quebec for local alerts. The AQHI (Air Quality Health Index) is the system used by Environment Canada and Health Canada; it focuses on risks to human health based on short-term exposure.
The two tools complement each other. The AQHI indicates when to avoid outdoor activities; the IQA, on the other hand, provides a more detailed breakdown of the pollutants present in your specific neighborhood, whether it’s Ville-Marie, Rosemont, or Laval.
How Outdoor Pollution Enters Montreal Homes
This is where many homeowners are surprised. We tend to think that closing the windows keeps us safe. Not quite.
Houses breathe. And in Montreal, with our freeze-thaw cycles, the walls, foundations, and joints are constantly expanding and contracting. This creates pathways for air infiltration—micro-cracks through which outside air enters, even without us noticing.
The Quebec winter effect: sealed-up homes, stagnant air
In winter, we seal our homes as tightly as possible to keep the heat in. That makes sense. But it means that stale air gets trapped inside.
CO2 levels in poorly ventilated homes regularly exceed 1,000 ppm, the threshold beyond which concentration and alertness begin to decline. In Montreal daycare centers, readings have averaged 1,333 ppm. Approximately 25 % of homes in the region do not meet minimum ventilation standards.
And in winter, indoor PM2.5 concentrations can be 50 % higher than in summer, precisely because the air isn't circulating.
Smoke from wildfires and seepage (2025)
Smoke from fires isn't just a temporary nuisance. PM2.5 particles from wildfires can seep into homes at levels ranging from 20 to 30 % of their outdoor concentration, even with doors and windows closed.
During the summer of 2025, certain areas of Greater Montreal recorded PM2.5 levels that were 24 % to 361 % above normal levels. In homes with wood-burning stoves or poor filtration systems, indoor levels exceeded WHO thresholds by 53.8 %.
HEPA filtration and a well-maintained air exchanger are the only two things that really make a difference under these conditions.
Are you wondering if your home is affected by outdoor air quality? Request a free inspection from the Vortex Air team, with no obligation, no pressure.
Real Impacts on Health and the Home
Poor indoor air quality isn't always obvious. But its effects build up over time.
Health Canada estimates that approximately 1,540 premature deaths per year in Canada are linked to air pollution. And the health costs associated with poor indoor air quality are estimated to range from 500 $ to 1,000 $ per household annually, in terms of doctor visits, medications, and lost workdays.
Prioritizing the Health of Families, Children, and Seniors
Children breathe faster than adults. As a result, their exposure to contaminants is proportionally higher. In a poorly ventilated home, this can worsen asthma, cause repeated respiratory infections, and interfere with sleep.
In older adults, the cardiovascular system bears the brunt of the impact. CO2 levels consistently above 1,000 ppm—as is common in many unventilated bedrooms—increase the risk of chronic headaches and unexplained fatigue.
Dampness and Mold: A Problem in More Than 55 % of Homes
Relative humidity that consistently exceeds 55 % is a direct invitation for mold. And in Montreal, with our humid summers and winters where condensation forms on cold windows, this threshold is often reached.
Mold settles in walls, under floors, and also in wall units and ventilation ducts. Once there, it releases spores into the air 24 hours a day, 7 days a week. Structural damage may take years to become visible, but the health effects begin long before that.
Real Estate Value and Perception of Risk
Homebuyers in Montreal are becoming increasingly aware of air quality issues. A home with a history of mold, ducts that have never been cleaned, or a faulty ventilation system can lose between 5 % and 10 % of its perceived value during a transaction.
In neighborhoods like Plateau-Mont-Royal or Ville-Marie, where older multi-unit buildings are common, this factor is becoming increasingly important. Buyers are now requesting inspection reports that include information on ventilation.
Common Myths About Indoor Air Quality
There are a lot of common misconceptions. There are three in particular that come up often.
«Indoor air is always cleaner in winter»
This is probably the most widespread—and most dangerous—myth. In winter, the outdoor air is indeed colder and often clearer. But indoors, the opposite is true: the air stagnates, contaminants accumulate, and PM2.5 levels can be 50 times higher than outdoors.
A well-heated but poorly ventilated house is like a closed room. The air just circulates in circles.
«Air fresheners improve air quality»
Aerosol air fresheners and fragrance diffusers do not purify the air; instead, they add volatile organic compounds (VOCs) to it. Even at low concentrations, these substances irritate the respiratory tract and contribute to the deterioration of indoor air quality.
If your home smells musty, it’s a problem that should be addressed at the source, not masked.
«Electric heating = clean air»
It’s true that electric heating doesn’t burn fuel. But it recirculates the existing air. If your ducts are clogged with dust, allergens, and debris, your heating system redistributes them throughout every room with each cycle. Whether it’s clean or not, it’s the same air that’s circulating.
Why Mechanical Ventilation Is Essential in Montreal
Mechanical ventilation is the only way to replace air in a controlled manner in a well-sealed building. And in Montreal, with our six-month-long winters, it’s not a luxury—it’s a necessity.
In daycare centers equipped with controlled mechanical ventilation, studies have shown a 44 % reduction in CO2 concentrations. Imagine what that means for your children, your sleep, and your concentration.
Signs That Your Home Is Poorly Ventilated
Here's what we often see when we work in homes in the Plateau, Laval, or Longueuil:
- Persistent condensation on the windows in the morning
- Musty or stale odors, even after cleaning
- CO2 levels above 1,000 ppm (measurable with an affordable detector)
- Allergies or respiratory irritation that improve when you're away from home
- Dust that quickly returns after cleaning
If you recognize two or more of these signs, your breathing deserves serious attention.
Solutions tailored to Quebec's climate
There’s no one-size-fits-all solution. What works in a new condo in Griffintown isn’t necessarily what’s needed in a 1960s triplex on the Plateau.
Here's what really makes a difference in our region:
The Air Exchanger, refreshes indoor air without losing heat. Essential in airtight buildings constructed after 2000.
Duct Cleaning, removes dust, allergens, and contaminants that have built up over several years. Should be done every 3 to 5 years, depending on usage.
HEPA Filtration, captures PM2.5 and mold spores. Particularly useful during smog or wildfire episodes.
Smart Sealing, seal actual air leaks without making the house stuffy. A thermal inspection can identify problem areas.
Want to know how your system is doing? Schedule a comprehensive assessment of your ventilation system with Vortex Air, it's free and there's no obligation.
Why choose Vortex Air in Montreal
We’re a local team. Mohamed and Omar, the two co-owners, are directly involved in every project. No unknown subcontractors, no vague promises—just a job well done by people who know Montreal.
For over 10 years, we’ve been serving homes and apartment buildings throughout Greater Montreal, from north to south, from Laval to Longueuil. More than 500 clients trust us. And we’re proud of that.
Our 4-Step Methodology
- Free inspection, We assess your system before giving you anything. No surprises, no high-pressure sales.
- Transparent Submission, You'll receive a clear, written quote before we get started. What we quote is what you pay.
- High-Power Cleaning, Our certified technicians use industrial-grade equipment to thoroughly clean ducts, wall-mounted units, dryer vents, and air exchangers.
- Final Check, We test, we measure, and we explain our findings to you. You'll leave with a clear report on the condition of your system.
Our Certifications and Standards
We are certified INVC, the Quebec standard for ventilation cleaning companies. We are also in the process of obtaining certification NADCA, the North American leader in HVAC system cleaning.
That means we follow strict protocols. No improvising, no cutting corners.
What Our Customers Say
»We've been living in an old apartment building on the Plateau for 12 years. After Vortex Air cleaned the ducts, we noticed a difference within a few days—less dust and fewer allergy symptoms for our son.», Client, Plateau-Mont-Royal
»Mohamed came to do the inspection himself. He was honest; he explained what needed to be done and what could wait. That's rare.», Client, Laval
Call now—service available 7 days a week in Montreal: 514-214-7492 Or book online: vortexair.ca
FAQ, Air Quality Index, and Homes in Montreal
Does outdoor air quality always affect indoor air quality?
Yes, but not immediately or uniformly. During episodes of smog or wildfire smoke, between 20 % and 30 % of outdoor fine particulate matter enters indoor spaces, even in closed homes. The rate of infiltration depends on the building’s airtightness and the quality of the filtration system.
How can you test the air quality in your home?
CO2, VOC, and PM2.5 detectors are available for between 80 $ and 300 $ at hardware stores or online. For a comprehensive assessment that includes mold and ventilation, a professional inspection provides a much more reliable picture.
Does smoke from fires linger in the vents for a long time?
Smoke particles can settle on the walls of air ducts and be recirculated for several weeks after an episode. Professional cleaning is recommended after a period of intense wildfires, especially if you have children or people with asthma at home.
Is indoor air more polluted in the winter?
Yes. In winter, the house is sealed off and air does not circulate naturally. Indoor PM2.5 concentrations can be 50 % higher than in summer. Without a functioning air exchanger, contaminants build up.
What level of CO2 is dangerous?
Above 1,000 ppm, you begin to feel the effects: fatigue, difficulty concentrating, and headaches. At 2,000 ppm and above, the effects become significant. The recommended standard for residential spaces is below 800 ppm.
Are the older Plex buildings on the Plateau at greater risk?
Yes, generally speaking. Buildings constructed before 1980 often lack built-in mechanical ventilation. Cracks and aging seals allow unfiltered air to seep in. And older materials can themselves release VOCs or moisture. It’s not inevitable, but it does require special attention.
How often should you clean the ducts?
For a home with no pets and no residents with allergies, every 3 to 5 years is generally sufficient. If there are pets, recent renovations, or a resident with respiratory issues, we recommend cleaning every 2 to 3 years. A severe wildfire can also warrant cleaning sooner.
Does the IQA affect resale value?
More and more, yes. Savvy buyers now ask for proof that the ventilation system has been maintained. A home with clean ducts, a properly functioning air exchanger, and a maintenance history sells better and is less likely to be subject to a price reduction.
Do you have any other questions about indoor air quality? Request your free inspection from Vortex Air, our team is available 7 days a week, from 7 a.m. to 9 p.m.
📞 514-214-7492 | ✉️ info@vortexair.ca | 📍 9187 Boulevard de l’Acadie, Montreal, QC H4N 3K1
