Improve indoor air quality

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Reduce air contaminants at the source

The most effective way to reduce indoor air pollution is to remove or reduce the source of contamination.


Make your home smoke-free by banning all tobacco products.

Dampness, water leaks and mould

Control humidity levels to avoid having too much humidity in your home. Too much humidity can cause mould to grow.

If you find mould, remove it yourself if it covers a surface area of less than 1 square metre. Remove mould on smooth surfaces with soap and warm water. There is no need to use bleach.

If mould cannot be removed from a surface easily, materials will need to be replaced. If the mould covers a bigger area, hire a professional to get rid of it.

You can reduce humidity by following these steps.

  • Fix leaks immediately.
  • Check hoses and connections for leaks and repair as needed.
  • Repair or replace cracked or damaged tile, grout and caulking around:
    • tubs
    • sinks
    • showers
  • Check plumbing pipes for condensation. If found, dry the pipes and seal with foam insulation.
  • Use a bathroom or kitchen exhaust fan when showering or cooking to reduce humidity. Keep the fan on for at least 30 minutes afterward.
  • Use a dehumidifier to remove water from the air, especially in the summer. Remove water from dehumidifiers when not in use so bacteria do not grow.
  • Remove water and anything wet immediately from your home if you have a flood. Dry out the area and any wet furnishings within 48 hours to prevent mould growth.
  • Keep curtains and blinds open to prevent condensation from forming on windows. Dry your window frames and sills daily if condensation is visible.
    • Condensation on windows may indicate low ventilation or high humidity in your home.

When washing or drying your clothes:

  • hang laundry outdoors to dry when possible
  • seal the joints in the dryer duct with foil tape
  • make sure that water flows directly into the laundry sink or drain
  • make sure your dryer vents to the outside and that it is not blocked

When storing items in the basement, use plastic bins with lids instead of cardboard boxes.

When cooking:

  • cover pots with a lid
  • use the exhaust fan
    • cook on the back burner so the fan can do a better job of lowering humidity

Household appliances

Make sure fuel-burning appliances are installed, maintained and working according to manufacturers' instructions. Have a qualified professional inspect them yearly, including chimneys and flues. These appliances can include:

  • gas water heaters
  • gas or oil furnaces
  • gas or wood stoves
  • gas or wood fireplaces


Cooking on the back burner and using the exhaust fan will help reduce particles and gases.

Follow these 3 tips for exhaust fans.

  1. Check the fans to make sure there is enough air movement.
  2. Make sure they are vented to the outside and not into the attic.
  3. Make sure nothing is placed in front of outside vents.

Activities that take place in an attached garage

Avoid idling your car, gas-powered lawnmower or snow blower in your garage. Pollutants can enter your home from the garage whether the garage door is open or closed.

House cleaning

Regular cleaning using a mix of methods can help improve indoor air quality.

  • Clean floors with a damp mop or cloth.
  • Clean the lint tray every time you use the dryer and check for lint build-up on the outside vent.
  • Use a mattress and pillow protector. Also vacuum mattresses and wash sheets once a week in hot water.
  • Vacuum often. Install a central vacuum that is vented outdoors. You can also use a vacuum with a high-efficiency particle air (HEPA) filter that traps small particles.

Improve ventilation

Ventilate your home by making sure there is good air circulation and heat flow. You can do this by:

  • leaving interior doors open
  • using bathroom and kitchen fans
  • keeping baseboards or heating vents clear of furniture
  • opening windows and doors when outside conditions are not smoggy
  • keeping beds, bedding and furniture away from outside walls to allow enough air and heat flow around furnishings
  • using a mechanical HVAC (heating, ventilation and air conditioning) system in your home with a filtration system built into the duct work
    • replace or clean the filter as per the manufacturer's instructions

When renovating, open the windows. Also make sure there is enough ventilation during major projects like:

  • cleaning
  • painting
  • varnishing
  • home improvement

Filter the air

Filtering the air can reduce some indoor air pollutants. But air cleaning is rarely effective on its own, and should be used alongside:

  • improving ventilation
  • reducing contaminants at the source

Portable air cleaners, particularly HEPA filters and electrostatic precipitators, can reduce some air contaminants. HEPA filters collect particle pollutants with a fine filter. But electrostatic precipitators collect pollutants with electrostatic energy, which causes pollution to stick to the filter.

Some air cleaners with electrostatic precipitators may also produce low levels of ozone, which can irritate the lungs. Ozone generators are sometimes marketed as air cleaners, but they are not recommended in homes.

Air cleaners can be effective in removing particles but most do not remove gases.

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If indoor air quality does not improve

Some people have more options for improving their indoor air quality than others. If you live in a multi-unit residence and have followed the listed actions without seeing an improvement:

  • talk to the building owner or management
  • check with your provincial or territorial government for information on the owner's responsibilities and your rights as a tenant
  • check with your municipal government, as some municipalities may have by-laws on acceptable standards for rental properties

Publications and reports

Causes of poor indoor air quality

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Combustion-related activities and sources

Indoor combustion-related activities can contribute to poor indoor air quality by giving off particles or gases.

Key indoor activities that can generate indoor air pollutants include:

  • smoking
  • heating
  • activities that take place in an attached garage
  • cooking


Cigarette smoke emits a wide range of chemicals, such as:

  • carbon monoxide (CO)
  • formaldehyde
  • volatile organic chemicals (VOCs), including benzene and formaldehyde
  • particulate matter


CO, nitrogen dioxide (NO2), VOCs and particulate matter can be emitted from appliances like:

  • gas and wood fireplaces
  • gas or oil furnaces
  • gas water heaters

Activities that take place in an attached garage

An idling car, starting your gas-powered lawnmower or snow blower, operating a generator or using a barbeque inside your garage emits:

  • CO
  • NO2
  • VOCs
  • particulate matter

These pollutants can enter the home when the garage door is open or closed.


Cooking methods like frying emit more particles than others and can also increase humidity levels. Cooking with a gas stove increases the amount of pollutants if a range hood is not used properly. Pollutants include particulate matter and NO2.

Non-combustion sources

Household items, personal care products, building materials and hobbies can also contribute to poor indoor air quality.

Household items

Household items can release gases such as VOCs, including formaldehyde, into the air in your home. This is known as off-gassing. Some items can also produce particles. Items that can release gases or particles include:

  • furniture and cabinets
  • carpets
  • candles and incense
  • cleaning products

Carpets, fabric, foam chair cushions, pillows and mattresses can also attract dust mites. These mites produce allergens.

Photocopiers and some portable air cleaners may also produce ozone.

Personal care products

Some personal care products such as cosmetics and perfumes can release chemicals into the air.

Building materials

Building materials can also release gases such as formaldehyde and other VOCs into the air. These materials include:

  • insulation
  • flooring
  • wood products
  • glues
  • solvents
  • paints and varnishes

It is important to follow the manufacturer's instructions for installation and use.


Different hobbies can release gases and particles. Hobbies that can contribute to indoor air pollution include:

  • woodworking
  • carving
  • arts and crafts

Dampness and water leaks

Areas where stagnant water builds up or damp places like showers and basements are sources for biological pollutants like:

  • bacteria
  • mould and fungi

High humidity, leaks, water infiltration and flooding conditions can cause mould to grow indoors.

Poor ventilation

Poor indoor air quality is affected by the level of ventilation in a building, such as:

  • how much fresh air is entering the building from outside
  • how effectively contaminated air is being exhausted from the house

Good ventilation removes stale indoor air and reduces the amount of indoor air pollutants. It also helps to limit the build-up of indoor moisture, which can contribute to mould growth.

Ventilation increases the amount of outdoor air that comes indoors. The level of outdoor air pollution should be considered when ventilating your house.

If there are strong indoor sources and outdoor air pollution levels are low, you may need to increase the ventilation.

During periods of high levels of outdoor air pollution, take measures to reduce air entering the home from outside. These include:

  • closing the window
  • turning on the air conditioning

Residential indoor air quality guidelines

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Summary of guidelines

The Residential Indoor Air Quality Guidelines summarize the health risks of specific indoor pollutants. They also provide information on:

  • known health effects of indoor air contaminants
  • indoor sources of air contaminants
  • recommended exposure limits
  • recommendations to reduce your exposure to pollutants

In some cases an exposure limit cannot be determined from the available scientific evidence. When this happens, a guidance document is developed that focuses on actions to reduce indoor exposure.

Summary of recommended exposure limits

The guidelines recommend exposure limits for contaminants that affect indoor air quality. These limits include:

  • long-term exposure limits
    • for health problems that can occur from continuous or repeated exposure over several months or years
  • short-term exposure limits
    • for health problems that can occur immediately after a brief exposure

The following guidelines or guidance have been developed for various contaminants. The recommended sampling time that this guideline is based on is shown in brackets:

  • acetaldehyde
    • long-term exposure limit (24 hours): 280 µg/m3 (157 ppb)
    • short-term exposure limit (1 hour): 1420 µg/m3 (795 ppb)
  • benzene
    • keep indoor levels of benzene as low as possible
  • carbon monoxide
    • long-term exposure limit (24 hours): 11.5 mg/m3 (10 ppm)
    • short-term exposure limit (1 hour): 28.6 mg/m3 (25 ppm)
  • formaldehyde
    • long-term exposure limit (8 hours): 50 µg/m3 (40 ppb)
    • short-term exposure limit (1 hour): 123 µg/m3 (100 ppb)
  • fine particulate matter (PM2.5)
    • keep indoor levels of PM2.5 as low as possible
    • use a stovetop fan (which exhausts outdoors) while cooking and do not allow smoking indoors
  • mould
    • address any water damage in residences within 48 hours to prevent mould growth; and,
    • address any visible or concealed mould growing in residential buildings
  • naphthalene
    • long-term exposure limit (24 hours): 10 µg/m3 (1.9 ppb)
  • nitrogen dioxide
    • long-term exposure limit (24 hours): 20 µg/m3 (11 ppb)
    • short-term exposure limit (1 hour): 170 µg/m3 (90 ppb)
  • ozone
    • long-term exposure limit (8 hours): 40 µg/m3 (20 ppb)
  • radon
    • exposure limit 200 Bq/m3
  • toluene
    • long-term exposure limit (24 hours): 2.3 mg/m3 (0.6 ppm)
    • short-term exposure limit (8 hours): 15 mg/m3 (4.0 ppm)

New guidelines are posted as more contaminants are assessed.

Health Canada has also identified Indoor Air Reference Levels (IARLs) for 25 different volatile organic compounds (VOCs) commonly found in indoor air.

Contact the Air Health Science Division office if you:

  • have questions about the Residential Indoor Air Quality Guidelines
  • would like to read the scientific assessments used to develop the guidelines
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