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| Square Footage | Furnace BTU |
|---|---|
| 1,000-1,200 sq. ft. Home | 40,000 - 60,000 BTU |
| 1,200-1,500 sq. ft. Home | 60,000 BTU |
| 1,500-1,800 sq. ft. Home | 60,000 - 80,000 BTU |
| 1,800-2,500 sq. ft. Home | 80,000 - 100,000 BTU |
| 2,500-3,500 sq. ft. Home | 100,000 to 120,000 BTU |
COVID-19 was declared a global pandemic in March 2020, and since then, medical professionals and researchers have been actively studying ways to slow the spread of the virus and improve air quality to reduce transmission risks.
Across Canada, provinces and territories have taken varied approaches to reopening, but many areas are now moving into more advanced stages. As Canadians spend more time indoors, there is growing interest in understanding the connection between indoor air quality and the transmission of COVID-19.
Research has shown that poor indoor air quality—due to insufficient ventilation, limited filtration, or low humidity—can increase the risk of transmitting airborne pathogens, including the coronavirus. This concern has prompted many homeowners and business owners to ask questions about how to improve indoor air quality and reduce exposure risks.
This guide explores the connection between COVID-19 and indoor air quality. It covers current research on virus transmission, the safety of indoor versus outdoor environments, the role of ventilation and filtration, systems that can improve indoor air quality, and common questions Canadians have about staying safe indoors.
While many people may feel fatigued hearing about SARS-CoV-2, the virus that causes COVID-19, understanding its spread remains essential.
Recent studies indicate that COVID-19 spreads primarily through aerosols and droplets released when an infected person coughs, sneezes, speaks, or even breathes. These droplets can either settle on surfaces or directly enter the noses, mouths, or eyes of people nearby.
This explains why measures like social distancing and mask-wearing are effective. Physical distancing reduces the chance of inhaling respiratory droplets, while masks help prevent the release of droplets into the surrounding air.
Current research suggests that aerosolized virus particles can remain airborne for up to three hours. This highlights the importance of improving air quality and circulation in indoor spaces to reduce exposure risks.
The virus can survive on surfaces such as glass, plastic, cardboard, and wood for up to 3.5 days. However, experts remain uncertain about how often surface contact actually leads to infection, or “fomite” transmission.
Most COVID-19 cases are linked to indoor settings, typically after prolonged exposure. Household transmission accounts for a significant portion of infections, followed by workplaces and public transit as common sites.
Studies show that respiratory droplets can travel over 2 metres when coughing and up to 8 metres when sneezing. Outdoors, sunlight, wind, and constant air movement help disperse droplets and reduce virus survival.
Although outdoor transmission is less common, it can still occur in crowded spaces. Social distancing and other precautions remain important, especially during events or busy public areas.
With schools, workplaces, and public spaces gradually reopening, Canadians are increasingly concerned about indoor safety, particularly during fall and winter when people spend more time inside.
One reason outdoor spaces lower infection risk is the presence of natural air currents. Indoors, air tends to be more stagnant, which can increase the risk of virus exposure. However, the type of HVAC system in a home or commercial building can make a difference in how air is circulated.
Boilers heat water and circulate it through radiators or pipes to warm a home. Since these systems do not move air, they provide little to no ventilation or circulation of indoor air. Because there is minimal air movement, contaminants such as viruses, dust, and allergens may remain suspended in certain areas, making supplemental ventilation or portable air purifiers more important in homes with boiler systems.
Ductless systems, also known as mini-splits, provide heating and cooling with an outdoor unit connected to one or more indoor air handlers. The system’s fans circulate air within the room, offering some air movement and localized ventilation. While effective for individual rooms, these systems do not evenly distribute air throughout an entire home, so pockets of stagnant air may still occur, highlighting the importance of combining them with proper ventilation strategies for better overall air quality.
Forced air systems, which include furnaces and central air conditioners, use ductwork and fans to circulate heated or cooled air throughout the house. These systems typically include basic filters to remove dust and debris, with higher-grade filters capable of capturing smaller particles and pathogens. Properly maintained systems with high-quality filters can significantly reduce indoor pollutants, but regular filter replacement and occasional professional duct cleaning are essential to ensure optimal air quality and prevent the spread of airborne contaminants.
While circulation helps, it is not enough to eliminate airborne pathogens. The goal is to remove contaminated air or dilute it with fresh outdoor air.
Pollutants, allergens, and other airborne contaminants also require effective ventilation and filtration. Bringing in fresh air and filtering indoor air is crucial for improving overall air quality.
Increasing ventilation can reduce virus concentration, but it may also distribute particles throughout a space if the air is already contaminated. Some early COVID-19 outbreaks in restaurants and workplaces were linked to air circulation patterns that inadvertently spread the virus.
Although HVAC systems can move pathogens, research shows that standard systems, including furnaces, do not kill viruses. Only specialized filters or purification systems have the potential to reduce pathogen levels effectively.
Even if your home’s ventilation is limited, several devices and techniques can improve indoor air quality:
It’s important to remember that while these methods can improve air quality, no solution guarantees complete protection from COVID-19 or other pathogens. Always refer to manufacturer specifications for any HVAC device.
Most HVAC systems include a basic filter, which captures large particles like dust. High-efficiency filters, such as HEPA filters, can trap much smaller particles (down to 0.3 microns).
While highly effective for allergens and bacteria, SARS-CoV-2 is smaller than 0.3 microns, so some virus particles may bypass even a HEPA filter.
When upgrading filters, consider the MERV (Minimum Efficiency Reporting Value) rating. A MERV 13 or higher filter is recommended for capturing smaller airborne pathogens. Keep in mind that higher-rated filters can restrict airflow if your HVAC system is not designed for them, so consulting a licensed technician is essential.
UV-C light can inactivate viruses, bacteria, and fungi. When installed in a furnace or air conditioning system, it can reduce airborne contaminants.
Caution: Only specific UV-C wavelengths are safe for use in HVAC systems, as inappropriate wavelengths can be harmful to skin and eyes.
UV-C systems work by disrupting the DNA or RNA of microorganisms, rendering them inactive. Regular maintenance is required to keep UV lamps effective, including cleaning and periodic bulb replacement.
Whole-home systems can be categorized as exhaust, supply, or balanced:
Exhaust systems remove indoor air but do not introduce fresh air, limiting air quality improvements. While they help reduce humidity and odors in areas like bathrooms or kitchens, they cannot replenish oxygen levels or dilute airborne pathogens. For optimal indoor air quality, exhaust systems are often combined with supplemental ventilation or portable air purifiers to ensure healthier living spaces.
Balanced systems are ideal for Canadian homes because they provide both fresh air and energy efficiency, helping to maintain comfortable indoor temperatures while reducing pollutant levels.
Heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) are advanced systems that provide excellent air quality while maintaining energy efficiency.
HRVs and ERVs are particularly valuable during Canadian winters when outdoor air is cold, as they allow homes to ventilate without significant heat loss. Proper sizing and installation by a licensed HVAC professional are essential to maximize performance.
Portable air purifiers are ideal for smaller areas or for homeowners on a budget. They can be moved between rooms and are effective at filtering particles in localized spaces.
When selecting a portable purifier, consider the Clean Air Delivery Rate (CADR), which measures the volume of filtered air delivered per minute. Choose a CADR suitable for the room size for best results. Some units also include carbon filters to reduce odours and VOCs (volatile organic compounds).
While these systems improve air quality, they may not fully prevent airborne virus transmission. Combining portable purifiers with other measures like mask-wearing and distancing offers the best protection.
Sometimes, the most cost-effective solution is the simplest: opening windows. Natural ventilation can help disperse lingering droplets and improve air quality, especially when temperatures are moderate.
If outdoor temperatures are too low, consider briefly opening multiple windows to create cross-ventilation, or using trickle vents if available. This approach increases air turnover and reduces the concentration of airborne pathogens indoors.
Maintaining proper indoor humidity is important for comfort and health. Air that is too dry can cause skin irritation, sore throats, and static electricity, while overly humid air can encourage mold growth and damage structures.
According to Health Canada, ideal home humidity ranges from 30% to 55%. Research suggests that COVID-19 transmission is lowest when indoor humidity is between 50% and 60%, as viruses spread more easily in cold, dry air.
Proper humidity also improves the comfort of occupants and protects furniture, wood floors, and electronics from extreme dryness or moisture.
Beyond ventilation, filtration, and humidity control, there are practical steps homeowners and business owners can take to improve indoor air quality and reduce COVID-19 transmission risk:
Children, seniors, and individuals with underlying health conditions are more susceptible to COVID-19. Homes, care facilities, and workplaces housing vulnerable populations should take extra precautions:
For business owners, ensuring proper indoor air quality can protect employees and customers:
Investing in indoor air quality measures can reduce absenteeism, improve comfort, and increase confidence among staff and clients.
Circulation alone is not sufficient. Effective ventilation and filtration, ideally combined, are necessary to reduce airborne pathogens.
Air quality is not easily detectable by sight or smell. Stale, stuffy air may indicate insufficient ventilation and airflow.
High-efficiency filters with MERV 13 or higher ratings, combined with HEPA filters where possible, offer the best protection.
Portable purifiers can supplement HVAC systems but are generally not sufficient alone for whole-home protection.
Maintaining indoor humidity between 50–60% reduces the virus’s ability to spread while keeping the environment comfortable.
Maintaining safe indoor air quality is essential for reducing COVID-19 risks in homes, workplaces, and commercial spaces. By combining proper ventilation, effective filtration, humidity control, regular maintenance, and practical safety measures, Canadians can create healthier environments that protect vulnerable populations, improve comfort, and enhance overall well-being.
For more information on energy efficiency standards and incentives in Canada, visit Natural Resources Canada.
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