Carbon monoxide kills more Canadians than any other indoor pollutant. It’s odourless, colourless, and produces flu-like symptoms that escalate to unconsciousness and death. Working CO detectors are the only defence.
Where does CO come from?
- Gas furnaces with cracked heat exchangers, blocked vents, or poor maintenance.
- Gas water heaters with backdrafting flues.
- Wood stoves and fireplaces with blocked chimneys or poor draft.
- Attached garages when cars idle inside — even briefly, the CO seeps through.
- Portable generators run inside or too close to windows.
- Gas BBQs or patio heaters used in enclosed spaces.
Symptoms of CO poisoning
Low-level exposure feels like the flu — headache, fatigue, dizziness, nausea, confusion. Higher levels add chest pain and impaired vision. Severe exposure causes loss of consciousness, seizures, and death. The flu connection is why so many cases are missed in winter.
If multiple family members feel sick at the same time, the pets seem off, and symptoms improve when you leave the house — assume CO until proven otherwise.
What to do if your CO alarm goes off
- Open windows and doors immediately.
- Get everyone out of the house — pets included.
- Call 911 from outside.
- Don’t re-enter until first responders or your gas utility says it’s safe.
- Don’t restart the suspected appliance until a technician has checked it.
Ontario’s CO alarm rules
Required outside every sleeping area in homes with any fuel-burning appliance OR an attached garage. See the full detector code summary for specifics.
Plug-in vs hardwired CO alarms
- Plug-in — cheap, easy, fine for retrofits in homes without panel-fed detectors.
- Hardwired with battery backup — gold standard. Interconnected so all alarms sound together. Doesn’t die when batteries run out. Required for new builds. Pricing.
Replace every 10 years
The electrochemical sensor wears out. After 10 years, even an alarm that beeps on the test button doesn’t actually detect. Mark the install date on the back — or buy alarms with a built-in “replace by” warning.
Maintenance
Vacuum the alarm vents once a year. Test the alarm with the button monthly. Replace batteries on battery-only models annually (or when the chirp starts).