Carbon dioxide in your home
Carbon dioxide (CO2) is an odourless, colourless and non-flammable gas. Learn about sources of CO2, its health effects and how to lower exposure to CO2 in your home.

On this page

  • Sources of CO2 in indoor air
  • Health effects of CO2
  • How to lower exposure to CO2 in your home
  • Exposure limit for CO2 in indoor air in Canada
  • CO2 values in other countries

Sources of CO2 in indoor air
Carbon dioxide is a pollutant found in indoor and outdoor air.

Indoors, CO2 is mainly produced through the respiration (breathing) of occupants, but can also come from:

  • cigarette smoking
  • unvented or poorly vented fuel-burning appliances

The level of CO2 in indoor air depends on 3 main factors:

  • ventilation
  • indoor sources of CO2
  • the outdoor CO2 concentration

The amount of indoor CO2 is often used:

  • as an indicator of general indoor air quality
  • to represent ventilation rate (the air changes per hour)

Outdoors, CO2 comes mainly from:

  • forest fires
  • combustion of fossil fuels
  • animal and plant respiration
  • organic matter decomposition

Health effects of CO2

As CO2 increases, you may be at increased risk of:

  • tiredness
  • headache
  • eye irritation
  • sore or dry throat
  • dizziness or difficulty concentrating
  • stuffy, congested or runny nose, sneezing, coughing and rhinitis

These effects may not be from CO2 exposure, but from poor indoor air quality in general.

How to lower exposure to CO2 in your home
You can lower levels of CO2 indoors by increasing ventilation and controlling the sources of CO2.
You can increase ventilation by:

  • opening windows when possible
  1. check the outdoor air quality conditions in your region before opening windows at Air Quality Health Index
  • using mechanical ventilation strategies. You can find more information on how to use both natural and mechanical ventilation to improve indoor air quality.

You can control indoor sources of CO2 by:

  • not smoking indoors
  • avoiding crowded living situations, if possible
  • using a range hood exhaust fan with outside venting when cooking
  • ensuring fuel-burning appliances are in good working order and properly vented
  • avoiding the use of unvented fuel-burning appliances (for example, space heaters) indoors

Exposure limit for CO2 in indoor air 
We developed an exposure limit for CO2 in homes based on:

  • CO2 sources
  • exposure levels
  • the health effects

The long-term exposure limit is 1800 µg/m3 or 1000 parts per million (ppm) based on a 24-hour average. This exposure limit:

  • indicates adequate ventilation
  • minimizes risks to human health from CO2 and other indoor air pollutants

This limit protects the health of Canadians including vulnerable populations such as:

  • Indigenous peoples
  • infants and children
  • individuals living in low income housing
  • those most susceptible to the effects of CO2 including individuals with pre-existing health conditions such as:
  1. asthma
  2. allergies
  3. cardiovascular conditions

The recommended exposure limit allows public health officials and other professionals to assess the risk from indoor air pollutants.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends maintaining indoor CO2 levels no greater than 700 ppm above ambient levels (assumed to range between 300 and 500 ppm).

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