Indoor Air Quality

Indoor air quality can impact your health. Urban Canadians spend almost 90 percent of their time indoors, meaning that most daily air exposure occurs in homes, schools, workplaces and other indoor environments. Indoor air quality is influenced by indoor sources such as mould, dust, allergens, smoke, household products and gases (e.g. carbon monoxide and radon), as well as outdoor factors including air pollution, temperature, humidity and wildfire smoke. The design, operation and maintenance of ventilation and filtration systems also impact indoor air quality.

Poor indoor air quality can contribute to respiratory and cardiovascular health risks, worsen exposure during wildfire smoke and extreme heat events and affect transmission risk for some respiratory infections in shared indoor spaces.

Understanding these factors can help you take steps to improve your indoor air quality and reduce exposure to pollutants.

Indoor air quality is affected by a mix of pollutants and conditions inside your home. Here are some common causes of poor indoor air:

  • Moisture and mould
  • Dust
  • Allergens (e.g., pollen, pet dander, dust mites)
  • Pests (e.g., cockroaches, rodents)
  • Smoke (tobacco, cannabis, wood smoke)
  • Gases (e.g., carbon monoxide, radon)
  • Household products
    • Cleaners
    • Paints
    • Fragrances
    • Candles
    • Incense
    • Oil diffusers
  • Cooking and gas appliances
  • Outdoor air pollution (including wildfire smoke entering indoors)

Start with these steps to make your air cleaner:

Reduce and remove pollutants indoors

  • Don’t smoke indoors.
  • Reduce the use of products that release strong fumes or chemicals.
  • Choose safer cleaning products, such as low- or- no-VOC paints and cleaners when possible.
  • When you cook, turn on your rangehood and open a window.
  • Store cleaning products, paints and solvents away from your main living area.
  • Keep the door that connects your home to your garage closed to prevent vehicle emissions and gas fumes from entering your home.
  • Ensure gas stoves, furnaces, fireplaces and other combustion appliances are properly installed, maintained and vented to the outdoors.

Let in fresh air and improve ventilation

  • Check current air quality conditions before opening windows and doors.
  • Open windows and doors when outdoor air quality is low risk.
  • Install window guards and balcony safety locks to help prevent falls, especially for children. Do not remove or adjust these safety features.
    • Be sure to watch children closely when windows or balcony doors are open.
  • Use fans to move air through the space and increase airflow.
    • Position fans in windows to bring in fresh air or push indoor air out, depending on outdoor air quality.
  • Be mindful of outdoor allergens when opening windows, especially if you have allergies.
  • Run kitchen and bathroom exhaust fans to remove indoor air.
  • Keep vents and air returns clear (e.g., don’t block with furniture).
  • For more information, visit Health Canada’s guidance on Ventilation and the indoor environment - Canada.ca

Filter indoor air

  • Run a portable air cleaner that is equipped with a high-efficiency filter.
  • Use high-efficiency air filters compatible with your HVAC system.
  • Use certified air cleaners (e.g., HEPA), if available.

Good ventilation and filtration can also help reduce the spread of respiratory illnesses indoors. Learn more about reducing respiratory virus spread.

Control moisture and mould

Maintain heating and ventilation systems

  • Replace air filters regularly (follow manufacturer recommendations, approximately every 3 months).
  • Set your heating, ventilation and air conditioning (HVAC) systems to recirculate indoor air during poor outdoor air quality periods.

Test air quality in your home

Some air quality risks can’t be seen or smelled and must be detected through testing and alarms:

Radon

  • Test your home for radon using a long-term test kit.
  • If levels are high, take steps to reduce radon exposure.
  • Learn more about radon and your health.

Carbon monoxide

  • Install certified carbon monoxide detectors on every level, near sleeping areas.
  • Test alarms regularly and replace batteries as needed.
  • Learn more about carbon monoxide safety.

Respiratory illnesses can spread more easily when people share indoor spaces. Good ventilation and filtration can help reduce the concentration of airborne particles, including particles that may contain pathogens like viruses.

Ventilation increases the amount of fresh air flowing into a space, while filtration removes particles from the air. Together, these measures can help reduce the spread of respiratory illnesses indoors. The effectiveness of ventilation and filtration depends on factors such as room size, occupancy, activities taking place and the ventilation measures used.

No single intervention fully prevents respiratory virus transmission. A layered approach includes:

  • Immunization
  • Staying home when sick
  • Hand hygiene
  • Masking where appropriate
  • Cleaning and disinfecting high-touch surfaces (e.g., door handles, counter tops, tables, light switches, sinks, faucets and electronic devices)
  • Cleaning and disinfecting soft surfaces (e.g., clothing, drapes, bedding)
  • Improving indoor air quality through ventilation and filtration

    Each layer of protection can help reduce virus spread and work best when used together. Learn more about these measures.

    The steps described in the How to Improve Indoor Air Quality section can also help reduce the spread of respiratory illnesses indoors.

    When outdoor air quality is poor, take steps to reduce polluted air entering your home and protect your health:

      Toronto Public Health helps protect indoor air quality by monitoring health risks and emerging evidence, responding to complaints and investigating health hazards, supporting outbreak prevention in indoor settings and working with other organizations to share information and coordinate action.

       

       

      Date modified: July 9, 2026