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Indoor air in Canadian homes can contain a range of pollutants at concentrations that, over time, affect respiratory function, cardiovascular health, and neurological performance. Many of these pollutants have no colour, odour, or immediate sensory signal. Understanding the sources, typical concentration ranges, and applicable Health Canada guidelines for each contaminant is the starting point for any assessment or remediation effort.
1. Radon
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It enters buildings through cracks in foundations, floor drains, construction joints, and gaps around service penetrations. Because radon is denser than air, it tends to accumulate in basements and lower floors.
Health Canada's current guideline is a long-term average concentration of 200 becquerels per cubic metre (Bq/m³). At levels above 200 Bq/m³, mitigation is recommended. A 2012 cross-Canada survey found a national geometric mean of approximately 47 Bq/m³, but results varied considerably by region — parts of Manitoba, Saskatchewan, New Brunswick, and Ontario show higher-than-average concentrations.
Health Canada estimates that radon is the leading cause of lung cancer among non-smokers in Canada, responsible for approximately 3,200 deaths per year.
Measurement is done with long-term alpha-track detectors (at minimum 91 days, preferably a full heating season) placed in the lowest occupied area of the home. Short-term electret ion chamber tests are available but are considered screening tools only. A certified C-NRPP (Canadian National Radon Proficiency Program) contractor can install and interpret detectors and recommend sub-slab depressurisation if levels exceed the guideline.
2. Carbon Monoxide
Carbon monoxide (CO) is produced by incomplete combustion of carbon-based fuels. In residential settings, sources include natural gas furnaces and water heaters, wood-burning fireplaces and stoves, attached garages, and portable generators operated indoors or near air intakes.
Health Canada's indoor air quality guideline for CO is:
- 11 ppm for exposure periods of 8 hours or more
- 25 ppm for 1-hour exposure
At concentrations above approximately 150 ppm, headache, dizziness, and disorientation develop within 2–3 hours. The Ontario Fire Code requires CO alarms on each storey and adjacent to sleeping areas in homes with fuel-burning appliances or attached garages. Alarms conforming to ULC-S588 are the applicable standard in Canada.
3. Volatile Organic Compounds (VOCs)
Volatile organic compounds are a chemically diverse class of carbon-based substances that vaporise at room temperature. Indoor sources in Canadian homes include:
- Paints, varnishes, and wood stains (alkyd- and oil-based formulations emit more than water-based)
- Adhesives and caulking products
- Composite wood products (plywood, MDF, particleboard) emitting formaldehyde from urea-formaldehyde resins
- Cleaning agents, air fresheners, and personal care products
- Dry-cleaned fabrics (tetrachloroethylene)
- New flooring materials, particularly vinyl and foam-backed carpet
Health Canada has set specific guidelines for formaldehyde (100 µg/m³ long-term) and toluene (300 µg/m³ for 24-hour exposure). Total VOC (TVOC) as a single metric has limited diagnostic value because the health implications differ significantly by compound.
Off-gassing from new building materials is highest in the first weeks after installation. Increasing fresh air exchange rates through opening windows or running mechanical ventilation at higher speeds during this period measurably reduces concentrations.
4. Particulate Matter (PM2.5)
PM2.5 refers to particles with an aerodynamic diameter of 2.5 micrometres or less — fine enough to penetrate deep into the lung and enter the bloodstream. Indoor sources include:
- Cooking (particularly frying, broiling, and use of gas ranges)
- Wood-burning fireplaces and stoves — a significant source in rural and suburban Canadian homes
- Candles and incense
- Tobacco and cannabis smoke
- Infiltration from outdoor air (particularly relevant during wildfire smoke events, increasingly common in Western Canada)
- Printer toner and 3D printing filaments
Health Canada's guideline for long-term PM2.5 exposure is 8 µg/m³ (annual average), aligned with the 2021 WHO Air Quality Guidelines. For 24-hour exposures, the guidance level is 27 µg/m³.
Low-cost optical particle counters (laser particle sensors) provide useful real-time data for identifying activity-related PM2.5 spikes, though their absolute accuracy varies by sensor model and ambient humidity.
5. Biological Contaminants
Biological contaminants include mould, bacteria, dust mites, and pet dander. Mould growth requires three conditions: a food source (any organic building material), moisture (surface water activity above 0.8 Aw), and a temperature range typically between 4°C and 35°C. In Canadian homes, moisture problems stem from plumbing leaks, basement flooding, condensation on cold surfaces during winter, and inadequate bathroom or kitchen exhaust ventilation.
There is no Canadian regulatory limit for airborne mould spore counts. Health Canada's guidance focuses on visible mould growth as an indicator requiring investigation and remediation regardless of species identification. Areas larger than 0.1 m² require professional remediation in most provincial guidelines.
Dust mites require relative humidity above approximately 50% at the sleeping surface to reproduce. Maintaining whole-home RH below 50% in summer significantly reduces viable mite populations. In winter, Canadian homes typically reach low RH naturally through cold dry air infiltration, which suppresses mite activity but may require humidification for occupant comfort.
6. Nitrogen Dioxide
Nitrogen dioxide (NO₂) is primarily an indoor concern in homes with gas ranges and unvented combustion appliances. Gas cooking can elevate kitchen NO₂ concentrations to 200–400 µg/m³ during and immediately after use — well above Health Canada's guideline of 100 µg/m³ (1-hour average) and 40 µg/m³ (annual average).
Range hood ventilation exhausted to the exterior (not recirculating-only charcoal filter hoods) is the most effective control. Minimum airflow for cooking exhaust per ASHRAE 62.2 is 100 cfm for range hoods directly above the cooktop, with specific placement guidance for island installations.
7. Summary: Health Canada Guidelines at a Glance
Radon
200 Bq/m³ long-term average. Test with alpha-track detector over minimum 91 days in lowest occupied area.
Carbon Monoxide
11 ppm (8-hour), 25 ppm (1-hour). Install ULC-S588 alarms on each storey with fuel-burning appliances.
Formaldehyde
100 µg/m³ long-term. Main sources: composite wood products and some adhesives.
PM2.5
8 µg/m³ annual, 27 µg/m³ 24-hour. Cooking and wood-burning are leading indoor sources.
