It's a question that's been asked a lot since 2020, and rightly so. We've all learned to be wary of the air we breathe in enclosed spaces. Building managers, CHSLD directors, condominium corporations - everyone wants to know: can the virus survive in our ventilation ducts and continue to circulate?
The short answer: no, COVID doesn't survive for weeks in your ducts. The virus inactivates quickly - in less than 3 hours, according to scientific studies. But that doesn't mean your ducts aren't important for air quality and respiratory disease prevention.
What really matters is how your ventilation system operates while people are present. A poorly maintained or filtered system can recirculate contaminated air between spaces, increasing the risk of transmission while an infected person is in the building.
In Montreal, with our long winters when everything stays closed, ventilation becomes critical. Studies show that the virus survives longer in the dry air of our heated homes. And many of our buildings - especially the older condos on the Plateau and in Rosemont - have outdated ventilation systems that recirculate too much air without enough filtration.
At Vortex Air, we've been working with building managers, schools and families for over 10 years. We've navigated the pandemic with them, seen the recommendations evolve, and understand the real concerns. In this guide, we'll untangle the myths from the facts, explain the real risks, and show you how to protect your indoor air effectively.
Understanding the link between COVID and ventilation systems
COVID-19 is transmitted mainly by droplets and aerosols - those tiny particles that remain suspended in the air for hours. That's where your ventilation system comes in.
A good ventilation system dilutes contaminants by continuously bringing in fresh outside air. It filters circulating air. It prevents excessive recirculation of stale air between different zones.
A poor system does the opposite: it recirculates the same air without sufficient filtration, it brings in little fresh air, and it can even redistribute contaminated air from one space to others.
The ducts themselves aren't really the problem. The virus doesn't survive long on duct surfaces. But dirty, clogged or poorly designed ducts reduce the overall efficiency of your system - and that's what increases the risk.
How COVID is transmitted in indoor air
When an infected person breathes, talks, coughs or sneezes, they release viral particles into the air. These particles come in two main sizes:
Visit large droplets fall rapidly to the ground - in a matter of seconds. That's why the 2-metre distance was recommended. These droplets don't travel far and don't really contaminate the ducts.
Visit aerosols are different. These ultra-fine particles (less than 5 microns) float in the air for hours. They can pass through an entire room, be drawn into the return air of your HVAC system, and potentially be redistributed elsewhere in the building.
A study published in the New England Journal of Medicine in 2020 showed that the SARS-CoV-2 virus (which causes COVID) has a half-life of around 1.1 hours in air. This means that after 1.1 hours, half the virus particles are inactivated. After 3 hours, almost all are inactive.
But here's the problem: if your system recirculates more than 70% of air (which is common in older buildings to save energy), this contaminated air can go through several complete cycles before the virus is inactivated. Meanwhile, it continues to circulate between spaces.
Dry air also increases the risk. In Montreal winters, indoor humidity often drops below 30%. In these dry conditions, aerosols stay in suspension longer, and the virus survives up to 20% longer than at 50% humidity.
Local example: Montreal schools and daycares with CO2 > 1000 ppm
CO2 measurements have become a key indicator of ventilation quality. When CO2 exceeds 1000 ppm (parts per million), the air is not sufficiently renewed.
Tests in several Montreal schools during the winter of 2022-2023 revealed CO2 levels regularly exceeding 1500 ppm in poorly ventilated classrooms. At these levels, the air children breathe has already been breathed in and out by others several times.
Day-care centers are particularly problematic. Small spaces, lots of children, and often minimal ventilation systems. If one child arrives infected in the morning, the whole class is exposed to high virus concentrations for hours.
Adding HEPA purifiers and improving ventilation in these spaces has shown measurable results. Absenteeism rates due to respiratory illnesses dropped significantly.
What Quebec experts say
The Institut national de santé publique du Québec (INSPQ) has published several clear recommendations on ventilation and COVID since 2020. Their message is consistent: ventilation is one of the most important measures for reducing transmission.
Health Canada recommends a minimum of 6 air changes per hour (ACH) for public spaces. Many Montreal buildings barely reach 2 to 4 ACH.
Patrick Levallois, an environmental health expert at the Université de Montréal, has pointed out in his research that improved ventilation reduces virus concentrations in indoor spaces by 30 to 50%. It's as effective as many other health measures, but gets less attention.
The Direction régionale de santé publique de Montréal has issued specific guidelines for seniors' residences and care facilities. Their recommendations include: increasing ventilation rates, improving filtration (minimum MERV 13), and ensuring regular system maintenance.
The evidence is clear: ventilation works. But it must be adequate, well maintained, and combined with good filtration.
Get a free duct inspection to assess your indoor air quality. At Vortex Air, we evaluate your current system, measure its efficiency, and recommend concrete improvements based on your situation. No charge, no obligation.
Myths and realities: COVID in air ducts
There's a lot of misinformation out there. Let's separate fact from fiction.
What is scientifically proven
FACT: HEPA filters capture 99.97% of particles 0.3 microns and larger
This is confirmed by Health Canada and validated by decades of research. The viral particles in COVID measure around 0.1 microns, but they usually travel attached to other, larger particles - exactly the size that HEPA filters effectively capture.
A properly sized and placed HEPA purifier can dramatically reduce airborne virus concentrations. This is particularly useful in poorly ventilated spaces where you can't easily upgrade the HVAC system.
FACT: An HRV (air exchanger) reduces viral concentration by 30% or more
By continuously bringing in fresh air from outside, an HRV dilutes contaminants. Even if an infected person is present, fresh air reduces the concentration of virus to which others are exposed.
Buildings with well-maintained HRVs showed significantly lower transmission rates during the pandemic. It's not a coincidence - it's basic physics: dilution equals risk reduction.
FACT: Professional duct cleaning removes 40% of accumulated allergens and particles
Clean ducts mean better airflow. Less resistance means your system can circulate more fresh air more efficiently. Accumulations of dust and debris reduce the overall efficiency of your ventilation system.
A clean, well-maintained system works as the engineers intended. A neglected system operates in degraded mode - often without you realizing it until an obvious problem arises.
FACT: Improving ventilation reduces all respiratory risks, not just VDIC.
It's important to understand this. Even if COVID becomes less of a concern over time, influenza, RSV and other respiratory illnesses will continue to circulate. A good ventilation system protects you from all these pathogens.
Investing in your ventilation means investing in the long-term health of your occupants. The benefits continue well beyond the pandemic.
Myths to debunk
MYTH: «The virus can live for months in the ducts».»
Completely false. The SARS-CoV-2 virus inactivates in less than 3 hours in air and on most surfaces. On metal (such as the inside of ducts), it can survive for a few days maximum under ideal conditions. But it rapidly loses its ability to infect.
Your ducts are not a long-term reservoir of active virus. However, they can be a vector of circulation while an infected person is present in the building.
MYTH: «Opening the windows for a few minutes is enough».»
Not good enough, especially in winter. Opening the windows helps temporarily, but as soon as you close them (which happens quickly when it's -20°C), you're back to the same problem.
And here's the thing: the very cold, dry outside air that enters paradoxically increases virus survival once warmed up inside. Relative humidity drops even further, creating conditions where aerosols remain suspended for longer.
The real solution is continuous mechanical ventilation - not sporadic bursts of cold air.
MYTH: «Chemical disinfection of pipes kills the virus».»
Disinfectants can actually kill the virus on surfaces. But spraying chemicals into your ducts poses several problems:
- The effectiveness is temporary - as soon as someone infected enters, you start all over again.
- Chemical residues can irritate occupants' respiratory tracts.
- It doesn't address the real problem: recirculation and inadequate filtration.
Proper ventilation and filtration are far more effective and sustainable than repeated chemical disinfection.
MYTH: «If no one is sick in the building, ventilation doesn't matter».»
Ventilation affects much more than just viral transmission. It also controls CO2, humidity, allergens, VOCs from building materials and cleaning products, and odors.
Good indoor air improves concentration, sleep and general well-being. Studies show that productivity increases in well-ventilated spaces. This is important 365 days a year, not just during a pandemic.
Download our free guide to post-COVID ventilation in Montreal. A complete PDF with expert recommendations, current standards, and an action plan to improve your system. Free and directly applicable to your Montreal reality.
Why are some Montreal buildings more at risk?
Not all buildings are equal when it comes to ventilation challenges. Certain types of structure and certain neighborhoods present higher risks.
Old HVAC systems and condos on the Plateau / Rosemont
The Plateau and Rosemont have thousands of condos created in old houses or triplex conversions. These buildings often date from the 1950s-1980s and have been renovated with limited budgets.
The result? Minimal HVAC systems. Many have only a heating system, with no real mechanical ventilation. Air circulates between units through old ducts and poorly sealed common spaces.
Approximately 30% of condos in these neighborhoods have never had a significant ventilation upgrade. They operate with an air change rate (ACH) of less than 4 - well below current recommendations for a minimum of 6.
During the pandemic, public health data showed a higher incidence of COVID cases up to 25% in these poorly ventilated buildings compared to newer constructions with adequate ventilation. It's not just a coincidence.
Condominium associations face a dilemma: improving ventilation is expensive, and convincing all owners to invest is difficult. But the cost of doing nothing - in health, work absences and quality of life - is probably higher in the long term.
Schools and CHSLDs: critical ventilation
Schools and retirement homes are two of the most critical environments for ventilation, and often among the least well-equipped.
A Université de Montréal study published in 2025 followed several elementary school that improved their ventilation. The results were impressive: a 25% reduction in average classroom CO2 corresponded to a 15% reduction in cases of COVID and other respiratory illnesses.
CHSLDs saw some of the worst results during the pandemic, due in part to inadequate ventilation. Many of these facilities date from the 1970s-1980s and were not designed with modern ventilation standards.
Shared rooms with a single air return create situations where one resident's air flows directly to the other. If one resident is infected, his or her roommate is exposed to high concentrations for hours.
Improvements made since 2020 - HEPA purifiers, increased ventilation rates, improved filtration - have shown measurable results. Outbreaks are less frequent and less severe in facilities that have invested in ventilation.
Local regulations and subsidies (TEQ, RénovVert)
The good news is that there are programs to help you improve your ventilation in Montreal and Quebec.
Transition Énergétique Québec (TEQ) offers grants of between 500 $ and 1,000 $ for the installation of energy-efficient air exchangers (HRVs). These systems improve your ventilation while recovering up to 85% of heat, reducing your heating costs.
RénovVert is a tax credit program for home renovation. Eligible work includes ventilation system upgrades. You can recoup a significant portion of your investment.
The City of Montreal has also launched initiatives to improve ventilation in municipal buildings, and offers technical support to private building managers who want to evaluate and improve their systems.
Adoption of MERV 13 or higher filters has reached around 65% in new systems or retrofits in Montreal. This is a major improvement - these filters capture far more fine particles than the old standard MERV 8 filters.
Quebec building code standards have also been tightened. Since 2012, all new residential buildings must have mechanical ventilation (HRV). For major renovations, similar requirements now apply.
Find out if your building is eligible for a TEQ grant to upgrade your ventilation. We can help you navigate available programs, assess your needs, and plan improvements. It's often less expensive than you think, especially with financial assistance.
How to sanitize your ducts and prevent virus recirculation
Let's move on to concrete solutions. What can you do now to improve your situation?
Best practices recommended by Health Canada
Regular maintenance of your HVAC system
Health Canada and INSPQ recommend a minimum of annual maintenance. This includes:
- Complete system inspection
- Filter cleaning or replacement (at least every 3 months)
- Checking air flow rates
- Cleaning accessible components
- Test the air exchanger if you have one
For deep duct cleaning, the general recommendation is every 3 to 5 years. But after an outbreak of respiratory disease in your building, additional cleaning may be warranted.
Upgraded filtration: HEPA or MERV 13+.
If your system can accommodate it, upgrade to MERV 13 or higher filters. These filters capture fine particles, including viral aerosols.
First check that your system can handle the increased resistance - over-restrictive filters can damage your equipment. A qualified technician can assess this easily.
Portable HEPA purifiers are an excellent complementary solution, particularly in poorly ventilated spaces where upgrading the central HVAC system is difficult or costly.
UV-C disinfection in pipes
Duct-installed UV-C systems can inactivate viruses and bacteria passing close to the lamp. This has been validated by the Canadian Centre for Occupational Health and Safety (CCOHS).
This technology is particularly useful in healthcare facilities, schools and commercial buildings. Installation generally costs between 800 $ and 2,500 $, depending on the complexity of the system.
Important: UV-C only works on what passes directly in front of the lamp. It is a complement to, not a replacement for, proper ventilation and filtration.
Increase ventilation rate
If possible, increase the percentage of fresh air in your system. Reducing recirculation and bringing in more outside air dilutes contaminants.
Yes, it adds slightly to your heating costs. But with an efficient HRV, heat loss is minimal. And the health cost of doing nothing is probably much higher.
The local solution: Vortex Air inspection and cleaning
At Vortex Air, we have adapted our services to meet the post-COVID concerns of our Montreal customers.
Free inspection and full assessment
We come to your home or building. We inspect your ducts with our endoscopic cameras. We evaluate your ventilation system: air flow, filtration, renewal rate.
We show you everything. Images of the inside of your ducts. The condition of your system. Problem areas. You see exactly what we see.
We then give you honest recommendations based on your actual situation. No fear-mongering, no unnecessary services. Just the facts and the options.
Certified cleaning with INVC/NADCA equipment
If cleaning is warranted, we use the suction-pulse method with HEPA filtration. Our equipment captures 99.97% of particles - nothing goes back into your air.
We are INVC certified and in the process of obtaining our NADCA certification. These certifications guarantee that we follow industry best practices for cleaning and decontamination.
Our technicians know the specific challenges of Montreal buildings. We've worked in Plateau condos with complex systems, schools with minimal ventilation, and modern buildings with high-tech systems.
Before-and-after photo report and full documentation
You will receive a detailed report with:
- Before and after photos
- Description of work carried out
- Recommendations for future maintenance
- Documentation for your files or insurance
This documentation is particularly useful for building managers and condominium associations who are accountable to owners or residents.
Plan your anti-virus maintenance with Vortex Air - free estimate 24/7. Call 514-214-7492 or visit vortexair.ca. We travel throughout Greater Montreal, and are available 7 days a week to answer your questions.
FAQ - COVID, ventilation and air quality in Montreal
Can COVID «live» in air ducts?
Not in the sense of a permanent reservoir. The virus inactivates in less than 3 hours in the air and in a few days on metal surfaces. Your ducts are not a habitat where the virus survives indefinitely. However, while an infected person is present, the virus can circulate in the system and be temporarily redistributed.
Does duct cleaning prevent transmission?
Cleaning alone does not prevent active transmission. What it does do is improve the overall efficiency of your system by removing obstructions and build-up. A clean system works better, circulates more air, and allows your filters to work more efficiently. It's one piece of the puzzle, combined with good filtration and ventilation.
What's the difference between HEPA purification and mechanical ventilation?
HEPA purification filters existing air by capturing particles. Mechanical ventilation (HRV) replaces stale air with fresh outside air. Ideally, you need both: ventilation to dilute and renew, purification to capture what remains. If you have to choose only one, ventilation generally has a greater impact on overall health.
How many times a year should I have my ducts inspected?
A basic visual inspection can be done annually, especially if your building is a high-risk one (schools, CHSLD, condos with a history of problems). Deep cleaning is recommended every 3 to 5 years under normal conditions. After an outbreak of respiratory disease or major renovations, an additional inspection is advisable.
Are MERV 13 filters sufficient against COVID?
MERV 13 filters capture around 85% of viral aerosol-sized particles. This is a major improvement over standard MERV 8 filters. For maximum protection, HEPA filters capture 99.97%, but not all systems can accommodate them. MERV 13 is an excellent compromise for most residential and commercial buildings.
Does air recirculation increase risk?
Yes, if excessive and poorly filtered. Recirculating 70-80% air without adequate filtration can redistribute contaminants. But a certain level of recirculation is necessary for energy efficiency. The key is balance: enough fresh air to dilute (minimum 20-30%), and good filtration on the recirculated air.
Is my HRV effective against viruses?
A well-maintained HRV is highly effective because it continuously dilutes contaminants by bringing in fresh air. It doesn't reduce the virus directly like a HEPA filter, but it does reduce the concentration to which people are exposed. It's a dilution rather than a capture strategy. The two approaches are complementary.
Are there any subsidies available in Montréal to improve ventilation?
Yes, Transition Énergétique Québec (TEQ) offers 500-1000 $ for the installation of energy-efficient HRVs. RénovVert offers tax credits for renovations including ventilation upgrades. The City of Montreal also has programs for certain types of buildings. Check your eligibility - you could save significantly on your investment.
Why choose Vortex Air for safe indoor air?
The pandemic has made us all more aware of the importance of the air we breathe. At Vortex Air, we take this responsibility seriously.
A certified local team with a human touch
We're not an impersonal franchise. We're a Montreal company, run by Mohamed and Omar, who have lived and worked here for over 10 years.
We've served over 500 customers - families, building managers, schools, businesses. We understand the specific challenges of our buildings, our climate, and our local regulations.
Our service is available 24 hours a day, 7 days a week. Because air quality problems don't wait for Monday morning. If you have a concern, we respond.
We're bilingual - French and English - because that's what Montreal is all about. You communicate in the language you're comfortable with.
Our transparent, safe method
Free, no-obligation inspection
We come and evaluate your system. Show you what we find. We explain the options. Then you decide if you want to proceed. Zero pressure, zero hard sell.
INVC-certified cleaning
Our technicians are trained and certified to the standards of the Institut National de Ventilation et de Climatisation. We follow established protocols to ensure safe and thorough cleaning.
We use professional equipment with HEPA filtration. Everything we remove from your ducts is captured - nothing gets dispersed into your building while we're working.
Before-and-after photos and clear report
You see the concrete results. We document the entire process. The report we give you includes images, details of the work done, and our recommendations for future maintenance.
This transparency is important to us. You've invested in your indoor air - you deserve to see exactly what you've achieved.
Montreal customer testimonials
Syndicat de copropriété, Rosemont: «Our 24-unit building dates back to 1975. We'd never had the ducts cleaned. After Vortex Air's inspection, we understood why several residents were complaining of respiratory problems. The cleaning made a huge difference. Complaints decreased by 80%. Professional service and reasonable price for a complete building.»
Daycare director, Laval: «With COVID, we were very concerned about ventilation. Vortex Air inspected our system, installed HEPA purifiers in the right places, and cleaned our ducts. Parents are reassured, and honestly, we've had fewer sick days this winter. It was worth every penny.»
**Building manager, Plateau:** «I manage three condos in the Plateau with outdated ventilation systems. Vortex Air was honest from the start - they told me exactly what was urgent and what could wait. No fear selling. They worked within my budget and constraints. Tenants breathe easier, and I have fewer complaints. I recommend them to all my fellow managers.»
The results speak for themselves. Our customers see:
- Reduced respiratory symptoms
- Less dust accumulation
- Fresher-smelling air
- Improved HVAC system performance
- Peace of mind
Call 514-214-7492 for a free inspection today. Or visit vortexair.ca to book online. We travel throughout Greater Montreal - Plateau, Rosemont, Laval, Longueuil, Brossard, North Shore and South Shore.
