By the Ventilation Vortex Air team—specialists in indoor air quality in Montreal
The summer of 2025 will be remembered as a landmark event. In June, the IQA in Montreal reached 164, a level that puts vulnerable people at real risk, even indoors. Across Canada, wildfires resulted in 57.1 million person-days of exposure in 2023, a record high. And 2025 further exacerbated the trend, with an estimated 20–30 % increase in PM2.5 concentrations in affected regions, including Greater Montreal.
The natural instinct is to close the windows and stay indoors. That's a good start. But it's far from enough.
Buildings in Montreal—especially apartment complexes built between the 1950s and 1970s—allow a significant amount of fine particulate matter to enter. And once inside, these particles remain there. Here’s what you need to know to protect your family, and what you can do about it.
Why Smoke from Wildfires Has a Significant Impact on Homes in Montreal
We tend to think that the walls of our homes protect us completely. In reality, a building’s airtightness can be measured, and many homes in Montreal don’t perform as well as we think they do.
The average infiltration factor for North American residential buildings is approximately 0.75. This means that 75 % of the fine particulate matter present outdoors eventually ends up indoors during a severe episode. During the worst days of the summer of 2025, indoor PM2.5 concentrations in unfiltered homes in the Montreal area reached approximately 31.5 µg/m³, well above the threshold recommended by Health Canada. Respiratory-related hospitalizations increased by 15 % in the weeks following the most intense smoke episodes.
Fine Particulate Matter (PM2.5): The True Invisible Danger
PM2.5 particles are the most concerning component of wildfire smoke. These particles are so small that they pass through the upper respiratory tract and reach the lungs directly—and even enter the bloodstream.
For people with an existing respiratory condition, the impact is 20 to 25 % more severe than for the general population. And among people aged 65 and older, they account for 35 % of pollution-related hospitalizations during smog episodes. What makes these particles particularly treacherous is that they are invisible. Even when the air indoors seems clear, PM2.5 levels can still be dangerously high.
Montreal, Laval, and the South Shore: Buildings That Are More Permeable Than We Think
Neighborhoods such as Plateau-Mont-Royal and Rosemont–La Petite-Patrie consist mainly of multi-unit apartment buildings constructed before 1970. These buildings were not designed to meet current waterproofing standards. The seals are deteriorating, the window frames are aging, and the foundations have micro-cracks.
In Laval and on the South Shore, newer single-family homes are better sealed, but their ventilation systems continuously draw in outside air without adequate filtration during smoke episodes. SOPFEU, which coordinates forest firefighting efforts in Quebec, issued several regional alerts in 2025 that directly covered the Greater Montreal area. Researchers from McGill University and the National Collaborating Centre for Environmental Health (NCCEH) documented these impacts on Quebec’s urban population.
Not sure how permeable your home is? Check your air infiltration level for free with an indoor air quality inspection by Vortex Air.
Myths and Facts About Indoor Smoking
There are many misconceptions that circulate during smoke events. Here are a few that we often hear.
Myth 1: Staying indoors is enough
This is the most widespread myth. And it is partially true—staying indoors reduces exposure. But with an infiltration factor of 0.75, between 45 % and 75 % of outdoor particles still enter. Without active filtration, indoor PM2.5 levels can exceed outdoor levels by 2 to 10 times after a few hours, especially when combined with indoor activities (cooking, cleaning).
Myth 2: If you can see the smoke, it's dangerous; otherwise, it's not
The absence of visible smoke doesn’t mean anything. PM2.5 fine particles are invisible to the naked eye. Even on a day when the air seems clear, the AQHI can still be cause for concern. Relying solely on what you see is a common mistake—and one that can be costly to your health.
Myth 3: Surgical masks provide protection
A surgical mask filters out large particles and droplets. It is not designed to filter PM2.5. Only properly fitted N95 or KN95 masks offer real protection against fine particles. This is an important distinction, especially for people who go outside briefly during an episode.
Gray Area: Do Pollutants Persist After the Event?
Yes, and this is a little-known fact. Studies have shown that concentrations of PAHs (polycyclic aromatic hydrocarbons) in homes double following episodes of heavy smoke. These compounds settle on surfaces and in vents. Data specific to Quebec is still limited, but the trends observed elsewhere in Canada and the United States are consistent. Cleaning the ducts after a major smoke episode is not an excessive precaution; it is a logical preventive measure.
Practical Solutions for Improving Indoor Air Quality During Smog Episodes
Here's what really makes a difference, in order of impact.
Step 1: Reduce infiltration (improvement of 30 to 50 %)
The first step is to limit the entry points. Close windows and doors as soon as an InfoSmog alert or a high AQHI is issued. Check the weatherstripping on exterior doors. Temporarily turn off your air exchanger if it does not have a HEPA filter or a recirculation mode.
These simple measures can reduce air infiltration by 30 % to 50 % in a typical home.
Step 2: HEPA filtration (50 to 80 % reduction in particles)
An air purifier equipped with a true HEPA filter is the most effective option available. It captures PM2.5 and spores with an efficiency rating of 99.97 % for particles 0.3 microns and larger.
The adoption of HEPA air purifiers in Quebec increased by 25 % in 2025, according to industry data. A high-quality air purifier for a bedroom costs between 200 $ and 500 $. For high-performance HVAC filters, expect to pay between 100 $ and 300 $; brands such as Camfil Canada offer options tailored to residential systems. Prioritizing the most frequently used rooms—the bedroom, living room, and children’s room—is the most effective approach.
Step 3: Cleaning Ducts and HVAC Systems
After a period of heavy smoke, the ducts trap particles, PAHs, and lingering odors. These residues continue to circulate throughout your home with every ventilation or heating cycle, long after the outdoor air has returned to normal.
That's where professional cleaning comes in. Not as a luxury, but as a logical step in the decontamination process.
4-Step Process, Vortex Air
- Inspection, We'll assess the condition of your ducts, check for particle buildup, and look for odors or visible deposits. It's free, and it takes about 30 minutes.
- Transparent Submission, Before you start anything, you'll receive a written quote. No surprises later on.
- High-Power Cleaning, Our technicians use industrial equipment that extracts and captures particles without dispersing them. For ducts affected by smoke, we adapt our procedure accordingly.
- Post-Service Inspection, We make sure the system is working properly and explain our findings to you. You’ll leave with a clear picture of your indoor air quality.
Protect your home before the next storm hits. Schedule your free inspection with Vortex Air today.
Local Context: Why Montreal Is Particularly Vulnerable
Montreal is unlike any other city when it comes to air quality. Several local factors combine to make our region more vulnerable than average.
InfoSmog vs. AQHI: Understanding Air Quality Alerts in Quebec
In Quebec, two parallel systems are used. InfoSmog is managed by Environnement Québec; it issues alerts based on local smog and fine particulate matter concentrations. The AQHI (Air Quality Health Index) is Health Canada’s federal system; it assesses health risks based on combined levels of ozone, NO2, and PM2.5.
During a smoke incident, both systems may be active at the same time. The rule of thumb: as soon as either system sounds an alarm, take action—close windows, use air filters, and limit intense physical activity indoors.
Winter, Firewood, and Atmospheric Stagnation
Smoke from wildfires is a summer problem. But indoor air quality in the winter is another challenge. Wood-burning stoves and fireplaces, which are still very common in Montreal’s older neighborhoods, contribute significantly to indoor air pollution during the cold season.
In January–February 2026, periods of atmospheric stagnation caused local emissions to become concentrated over the island of Montreal for several days. Under these conditions, households that heat with wood without properly maintaining their ventilation systems contribute to air pollution, affecting both themselves and their neighbors.
Schools, Daycare Centers, and Multi-Use Facilities: Specific Challenges
For families with young children, the issue of air quality in daycare centers and schools is a real concern. Older institutional buildings often have the same air infiltration problems as residential apartment complexes. For building managers on the South Shore or in Laval, the obligations to maintain ventilation systems are becoming increasingly important, both ethically and legally.
Do you manage a building or have specific concerns? Speak directly with a local INVC-certified specialist from the Vortex Air team.
Why choose Vortex Air to protect your indoor air?
We’re a local company. Our team is familiar with Montreal housing, the old ductwork in Rosemont’s multi-unit buildings, the ventilation systems in Longueuil homes, and the air exchangers in Laval’s newer condos. For over 10 years, we’ve served more than 500 clients throughout the Greater Montreal area.
We are certified INVC and currently undergoing certification NADCA, the two industry leaders in ventilation cleaning. Our technicians follow rigorous protocols, and our services are documented.
Prevention and Energy Efficiency Approach
A clean ventilation system doesn't just protect your health. It also reduces your energy consumption by 10 % to 15 %, because a system that's free of obstructions doesn't have to work as hard to circulate air.
Protection of Vulnerable Families
We tailor our methods to each household’s specific needs. For households with children, seniors, or people with respiratory conditions, we choose approaches that avoid irritants and plan our work to minimize disruption. After all, a family with an asthmatic child in Hochelaga-Maisonneuve doesn’t have the same needs as a single homeowner in a newly built condo.
Your indoor air quality deserves a thorough assessment. Book your indoor air quality assessment with Vortex Air today.
📞 514-214-7492 (available 24 hours a day) | Open 7 days a week, from 7 a.m. to 9 p.m.
FAQ: Wildfire Smoke and Indoor Air Quality in Montreal
How can I tell if smoke is getting into my house?
The most common signs: a faint smell of smoke indoors even with the windows closed, eye or throat irritation for no apparent reason, or a high reading on a PM2.5 detector (ranging from 80 $ to 250 $). If you don’t have a monitor, a professional inspection can assess how airtight your home is.
How long do the particles stay inside?
Without active filtration, for hours or even days. Fine particles remain suspended in the air for a long time, and those that settle on surfaces or in ducts can be recirculated by air movement. Cleaning the HVAC ducts and filters after a major event is recommended.
Is closing the windows enough?
This is necessary, but not sufficient. With a typical infiltration factor of 0.75, a significant proportion of particles still enters through the building’s micro-gaps. Active filtration—such as a HEPA purifier or a high-performance HVAC filter—is essential to complement passive sealing.
What is the difference between a HEPA filter and a standard filter?
A standard filter (such as basic HVAC filters) traps large particles, visible dust, and fibers. A true HEPA filter captures 99.97% of particles 0.3 microns and larger, including PM2.5. During episodes of smoke, only HEPA filters offer real protection against fine particles.
Should I clean my vents after a period of heavy smoke?
If the episode lasted several days and had a high IQA, then yes—especially if you noticed a lingering odor or if members of your family experienced respiratory symptoms. The ducts can trap PAHs and combustion byproducts that continue to circulate long after the episode has ended.
Are children and the elderly at greater risk?
Yes, significantly. Children breathe more rapidly, and their immune systems are still developing. People aged 65 and older account for 35 % of hospitalizations related to episodes of air pollution. For these two groups, preventive measures—such as filtration, duct inspections, and limiting exposure—are particularly important.
Do air purifiers work in the winter, too?
Absolutely. In winter, when the house is sealed up, a HEPA air purifier is even more useful—it treats the recirculated air that accumulates indoor contaminants. During periods of winter air stagnation in Montreal, a purifier in the bedroom can make a measurable difference in sleep quality and respiratory symptoms.
Do you have any other questions about your indoor air quality? Request a free inspection from the Vortex Air team, we're 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
