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Carbon monoxide poisoning – the silent killer

Odourless, colourless and deadly – here are the symptoms, and how to avoid exposure.

What is carbon monoxide?

Carbon monoxide is an odourless and colourless gas that can cause serious health problems if inhaled. Carbon monoxide can rapidly accumulate in the blood, reducing blood's ability to carry oxygen.

Symptoms of carbon monoxide poisoning

You may suffer from: headaches, nausea, general lethargy, dizziness, or flu-like symptoms that appear to get better when you are away from the area.

Where does carbon monoxide come from?

Carbon monoxide is a by-product of burning fossil fuels including natural gas, oil, propane, and wood.

In your home, a fireplace or a furnace can be sources of carbon monoxide, but if installed properly and maintained regularly, they will produce very little as a by-product. Carbon monoxide becomes an issue if your venting is blocked or if your heating equipment is damaged.

A defective heat exchanger in a furnace can also be a source of carbon monoxide. The danger arises if carbon monoxide escapes from the defective heat exchanger and mixes with the air circulated through the vents in your home.

What can I do to prevent carbon monoxide in my home?

Ensure you have working carbon monoxide detectors inside your home. It is recommended to have one in your basement near any heating equipment and others on the main and/or second level of your home. Carbon monoxide detectors are available at most home improvement stores.

Seek professional assistance

  • Have a qualified technician inspect and clean your fuel-burning appliances yearly before the cold weather sets in to ensure they are in good working order.
  • Have a qualified technician inspect chimneys and vents yearly for cracks, blockages (for example, bird's nests, twigs, old mortar), corrosion or holes.
  • Check your fireplaces for closed or blocked flues.
  • Check with a qualified technician before enclosing any heating or gas burning hot water equipment in a smaller room, to ensure there is adequate air for proper combustion.
  • Never use propane or natural gas stove tops, ovens or barbecues to heat your home.


As of October 2014, there are laws that make it mandatory for most Ontario homes which have at least one fuel-burning appliance, like a gas furnace or gas water heater, to have a carbon monoxide detector installed. Visit the Ontario Fire Marshall for more details.

Legal notes: Read the fine print.

The contents of this webpage are provided for general informational purposes only. We do not make any warranties about the completeness, reliability or accuracy of the information as it relates to your circumstances. Any action you take upon the information provided is strictly at your own risk. This information is not a substitute for, and is not intended to replace, independent professional advice. It is your responsibility to take all safety precautions and to refer to the product manufacturer's instructions or contact a licensed technician, as appropriate.