Indoor air quality concerns in Canadian homes fall into two broad categories: gaseous pollutants (radon, carbon monoxide, VOCs, nitrogen dioxide) and particulate pollutants (mold spores, dust mite debris, pet dander, combustion particles). The distinction matters because the approaches to addressing each are different — gaseous pollutants require source control or ventilation, while particulate pollutants can additionally be captured by filtration.
This guide covers the most commonly encountered indoor air pollutants in Canadian residential settings, their typical sources, the exposure levels considered concerning by Health Canada, and the practical options for reducing each.
Radon
Radon is a naturally occurring radioactive gas that forms as uranium in soil and rock decays. It is present in soil across most of Canada, and it enters homes primarily through cracks in foundation walls and floors, construction joints, gaps around service pipes, and through sumps. Radon has no odour, colour, or taste — it cannot be detected without a test.
Canada has among the highest residential radon concentrations of any country in the world. Health Canada's Action Level is 200 Bq/m³. Above this level, mitigation is recommended. About 7% of Canadian homes have radon levels above the action level, with higher rates in certain provinces including Manitoba, Saskatchewan, New Brunswick, and parts of Ontario and British Columbia.
Testing
Health Canada recommends testing all homes, regardless of age or location. Long-term tests (minimum 91 days, ideally a full heating season) in the lowest occupied level are the most accurate. Alpha-track detector kits are available at hardware stores and online, typically for $30–$60. Certified measurement contractors can also conduct tests.
Mitigation
Active soil depressurisation (ASD) is the most effective mitigation method. A pipe is installed through the foundation slab, connected to a fan that exhausts soil gas to the outdoors before it enters the home. Professional installation typically costs $1,500–$3,500 in Canada and can reduce radon levels by 80–99%. Increasing mechanical ventilation can also reduce radon concentrations by dilution but is generally less effective than ASD for high radon levels.
Carbon monoxide
Carbon monoxide (CO) is produced by the incomplete combustion of carbon-based fuels. In Canadian homes, the primary sources are gas furnaces, boilers, water heaters, fireplaces (gas and wood), gas stoves, and vehicles in attached garages. CO is colourless and odourless, and at high concentrations it is acutely toxic; at lower concentrations it can cause symptoms that are often mistaken for flu or food poisoning.
Health Canada's guidance specifies a maximum exposure of 11 ppm over 8 hours and 25 ppm over 1 hour for residential settings.
Detection
CO detectors are required by law in most Canadian provinces in homes with attached garages or any fuel-burning appliances. They should be installed at breathing height (not near the ceiling, where CO mixed with room air distributes evenly) and at a minimum on each sleeping level. CO detectors should be replaced every 5–7 years, as the electrochemical sensor degrades over time.
Reduction
Annual servicing of combustion appliances by a licensed HVAC technician is the primary prevention measure. The technician inspects heat exchangers for cracks (the leading cause of CO intrusion from furnaces), checks burner adjustment, and verifies proper flue gas exhausting. Ensuring adequate combustion air supply to gas appliances is also critical — sealed utility rooms without make-up air can cause appliances to produce elevated CO.
Volatile organic compounds (VOCs)
VOCs are a broad class of carbon-based chemicals that evaporate at room temperature. Indoors, they originate from an extensive list of sources: paints, varnishes, adhesives, new flooring materials (particularly vinyl and engineered wood with formaldehyde-based binders), cleaning products, personal care products, air fresheners, tobacco smoke, and dry-cleaned clothing.
Some VOCs — benzene, formaldehyde, naphthalene — are classified as carcinogens. Others cause acute symptoms at higher concentrations (headaches, dizziness, eye and throat irritation) or contribute to longer-term respiratory issues at lower chronic exposure levels. Health Canada has established indoor air quality guidelines for specific VOCs including formaldehyde (50 µg/m³ over 8 hours) and benzene (2 µg/m³ over 24 hours).
Sources and source control
New construction and recent renovations are the highest-emission periods. Off-gassing from materials like pressed wood products, carpet adhesives, and solvent-based paints is highest in the first weeks to months and declines over time. Strategies to reduce VOC exposure during and after renovation include:
- Selecting low-VOC or no-VOC paints, finishes, and adhesives
- Maximising ventilation during and immediately after installation of new materials
- Choosing solid wood flooring or ceramic tile over composite products where formaldehyde-based binders are a concern
- Airing out dry-cleaned items before bringing them indoors
- Storing paints, solvents, and cleaning products in a garage or outdoor shed rather than inside the home
Ventilation and activated carbon filtration
Mechanical ventilation (HRV or ERV) dilutes VOC concentrations by introducing outdoor air. For acute high-concentration situations — during painting or immediately after flooring installation — temporary direct ventilation via open windows combined with fans exhausting air to the outdoors is more immediately effective than filtration.
Activated carbon filters in portable air purifiers adsorb gaseous VOCs onto a carbon surface. The capacity of the carbon bed and the specific VOCs present determine how long the filter remains effective. These are useful as a supplement for chronic low-level VOC management but are not a substitute for reducing the emission source.
Mold and biological pollutants
Mold spores are present in outdoor air across Canada and inevitably enter homes through normal air exchange. The question is not whether spores are present but whether indoor conditions allow them to germinate and form colonies. Elevated humidity, the presence of organic material (wood, paper, fabric, food residues), and temperatures above 5°C create the conditions for mold growth.
Mold produces spores and mycotoxins that become airborne and can cause respiratory irritation, allergic reactions, and in sensitive individuals, more severe health effects. The most common indoor molds in Canadian homes are Cladosporium, Penicillium, and Aspergillus species. Stachybotrys ("black mold") is less common but associated with chronic water damage.
Prevention
Controlling relative humidity below 55% is the most effective prevention measure. Fixing water leaks promptly, ensuring exhaust fans in bathrooms and kitchens are ducted to the outside (not to attic spaces), and maintaining adequate ventilation in basements and crawl spaces reduce the moisture levels that mold requires. Bathroom exhaust fans should run during and for at least 20 minutes after showering.
Remediation
Small areas of mold growth (under 0.93 m² / 10 square feet) can be cleaned with soap and water or a low-concentration bleach solution on non-porous surfaces. Porous materials (drywall, insulation, carpet) that have sustained mold growth require removal and replacement rather than surface cleaning. Larger infestations warrant professional remediation to avoid dispersing spores during cleanup. Health Canada's guide on dampness and mould provides detailed remediation guidance.
Combustion particles and wood smoke
Wood-burning fireplaces and stoves are a significant source of fine particulate matter (PM2.5) and polycyclic aromatic hydrocarbons (PAHs) indoors when not properly vented. A poorly sealed fireplace insert, a chimney with negative pressure, or simply opening a wood stove door to add wood can introduce combustion particles to indoor air.
The EPA and Health Canada consider PM2.5 one of the most significant health-relevant air pollutants because particles in this size range penetrate deep into lung tissue. In Canada, wood smoke is also an outdoor air quality issue in communities with high wood heating use, and the outdoor-to-indoor transport of wood smoke during smoke events (whether from wildfires or neighbourhood wood burning) can raise indoor PM2.5 levels in homes relying on natural ventilation.
During regional smoke events, closing windows and running a MERV 13 furnace filter or a portable HEPA unit is the most practical response for homes without mechanical ventilation. Homes with HRVs should be aware that some units lack fine particle filters on the intake — adding a MERV 8+ filter to the HRV intake is possible on many models with appropriate adapters.
Asbestos and lead
Homes built before 1990 in Canada may contain asbestos in insulation, floor tiles, ceiling tiles, duct wrap, and some textured ceiling coatings. Intact, undisturbed asbestos-containing materials do not typically release fibres into the air; the hazard arises during renovation work that cuts, sands, or otherwise disrupts these materials.
Lead-based paint was common in homes built before 1978. Like asbestos, intact lead paint is generally a low immediate risk; the hazard increases when surfaces deteriorate or are disturbed during renovation. For homes of this vintage, it is standard practice to test for both asbestos and lead before undertaking major renovation work.
Both asbestos and lead abatement in significant quantities require licensed professionals and specific disposal procedures under provincial environmental regulations.
Related reading
- Choosing an air filtration system — which filter ratings capture mold spores and combustion particles
- Humidity control — the most important factor in mold prevention