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
- 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 in Canada
We developed an exposure limit for CO2 in Canadian homes based on:
- CO2 sources
- exposure levels
- the health effects
The long-term exposure limit is 1800 µg/m3 or 1000parts per million (ppm) based on a 24-houraverage. 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:
- asthma
- allergies
- cardiovascular conditions
The recommended exposure limit allows public health officials and other professionals to assess the risk from indoor air pollutants.
CO2 values in other countries
Canada's long-term exposure limit (1000ppm) is in line with standards from other countries and organizations.
Countries with established standards or guidelines for CO2 of 600to 1000ppm include:
- Korea
- Japan
- France
- Norway
- Portugal
- Germany
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends maintaining indoor CO2 levels no greater than 700ppm above ambient levels (assumed to range between 300and 500ppm).
Related information
- Residential indoor air quality guidelines: Carbon dioxide
- Guidance for Cleaner Air Spaces during Wildfire Smoke Events
- Housing suitability
- If you have questions about the guidelines for CO2 in indoor air, you can contact us at:
- 1-833-223-1014 (toll free)
- hc.air.sc@canada.ca
