When it comes to carbon monoxide (CO) safety, we all have a role to play in protecting ourselves, our families and our communities.
Carbon monoxide is a serious and potentially deadly hazard, but with proper prevention, maintenance and alarms, CO-related incidents are preventable.
What is Carbon Monoxide?
Carbon monoxide is a colourless, odourless, tasteless and toxic gas, often referred to as the “silent killer.” Because it cannot be seen or smelled, people may be exposed without realizing it.
When inhaled, carbon monoxide prevents oxygen from being carried through the bloodstream. High levels can poison the body quickly, while lower levels can cause harm over longer periods of time.
What are the symptoms of carbon monoxide poisoning?
Exposure to CO can cause flu-like symptoms such as
- Headaches
- Nausea
- Dizziness
- Burning eyes
- Confusion
- Drowsiness
- Loss of consciousness
In severe cases, CO poisoning can cause brain damage and death.
The elderly, children and people with heart or respiratory conditions may be particularly sensitive to CO.
How is carbon monoxide generated in the home?
Carbon monoxide is a by-product of incomplete combustion of fuels such as natural gas, propane, heating oil, kerosene, coal, charcoal, gasoline or wood.
This incomplete combustion can occur in any device that depends on burning for energy or heat, such as
- Furnace
- Gas water heater
- Gas fireplace
- Gas stove
- Gas dryer
- Gas barbecue
- Portable generators
- Fuel-burning space heaters
- Any gas-powered vehicle or engine
- Automobiles left running in attached garages
- Gas barbecues operated inside the house
- Grills or kerosene heaters that are not properly vented
- Chimneys or vents that are dirty or plugged
When fuel-burning appliances are properly installed, maintained and vented, carbon monoxide is safely exhausted outdoors.
Most Ontario homes contain four to six appliances capable of producing carbon monoxide.
The best way to reduce the risk of CO exposure is to eliminate it at the source:
- Have all fuel-burning appliances inspected annually by a trained and certified technician
- Keep vents and chimneys clear of snow, ice and debris
Carbon monoxide alarm requirements
Under the Ontario Fire Code, new carbon monoxide alarm requirements came into effect on Jan. 1, 2026.
Carbon monoxide alarms are required in homes that have:
- A fuel-burning appliance
- A fireplace
- An attached garage
CO alarms must be installed:
- Outside all sleeping areas and on every level of the home, including basements
In multi-unit residences they must be installed:
- If the building has a service room and the unit is located directly above, below or beside the service room.
- If the building has a garage and the unit is located directly above, below or beside the garage.
- If the unit is heated by air from a fuel-burning appliance that is not located within the unit, such as heated air coming from a furnace in a building service room.
- If hallways or corridors are heated by a fuel-burning appliance, carbon monoxide alarms must be installed in those areas at intervals not exceeding 25 metres.
Where should a CO alarm be located in the home?
- Outside all sleeping areas and on every level of a home or cottage
- In a recreational vehicle and boat cabin
- In a boathouse
Proper placement of a CO alarm is important. In general, the human body is most vulnerable to the effects of CO during sleeping hours, so an alarm should be located in or as near as possible to the sleeping area of the home, as well as every level of the home.
If only one alarm is being installed on that level, it should be located outside the sleeping area, where it can wake you if you are asleep.
Where sleeping areas are located in separate parts of the level, an alarm should be provided outside each area.
Unlike smoke, which rises to the ceiling, CO mixes with the air. Recognizing this, a CO alarm should be located at knee height (which is about the same as prone sleeping height). Due to the possibility of tampering or damage by pets, children, vacuum cleaners and the like, it may be located up to chest height. To work properly, a CO alarm should not be blocked by furniture, draperies or other obstructions to normal airflow.
If a combination smoke/carbon monoxide alarm is used, it should be located on the ceiling, to ensure that it will detect smoke effectively.
Always refer to the manufacturer's instructions for additional information regarding proper installation, use and maintenance.
Alarm testing
- Test carbon monoxide alarms once a month using the test button
- Replace batteries at least once a year, including back-up batteries for plug-in alarms
- A helpful reminder is to change batteries when the clocks are changed
CO alarms do not last forever. Most units must be replaced after seven to 10 years. Always check the manufacturer’s instructions.
Remember
Carbon monoxide is preventable. Working alarms, proper appliance maintenance and safe habits can save lives.
If the carbon monoxide alarm sounds:
- Get everyone outside to fresh air immediately
- Call 9-1-1 from outside if anyone is experiencing symptoms
Visit the TSSA's ‘silent killer’ page for more information on CO and how to protect yourself.