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Carbon Monoxide Detector Going Off: Leave the House First

Get everyone out of the building now. Once you're outside, call 911, and for a gas smell also call ATCO at 1-800-511-3447.

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A local furnace technician will call you back as soon as possible. If this can't wait, call other furnace technicians too.

What to do right now

  1. Get everyone out to fresh air

    Go now. Don't stop to gather belongings.

  2. Don't look for the source

    Health Canada says not to try to locate the source of carbon monoxide. Leave the furnace alone.

  3. Call 911 from outside

    Use your phone once you're out of the house, or borrow a neighbour's.

  4. Smell gas too? Call ATCO as well

    From outside, call ATCO's gas emergency line at 1-800-511-3447. Inside, don't touch switches and don't make calls.

  5. Stay out until you're told it's safe

    Calgary Fire says not to go back in until the fire department tells you it is safe to do so.

  6. Afterwards: get the furnace checked

    Even if the furnace starts again, have a professional check it before you count on it for heat.

Snow-covered house with spruce trees.
A house after snowfall.

Carbon monoxide detector going off: do this now

Smell gas, or is a carbon monoxide (CO) alarm going off? Get everyone out of the building now.

Don't stop to open windows, look for the leak or grab things. Leave lights and appliances alone on the way out.

Once you're outside, call 911. For a gas smell, also call ATCO's gas emergency line: 1-800-511-3447.

Treat a CO alarm as real, even if everyone feels fine. You can't see or smell carbon monoxide.

Don't go back inside until the fire department says it's safe, or a professional has fixed the problem.

Headache, dizziness, feeling sick or very sleepy, especially if others in the home feel it too? Get out and call 911.

This website is not an emergency service. If anyone is hurt or in danger, call 911.

This website's number is not for carbon monoxide emergencies. Call 911.

Carbon monoxide detector going off near furnace: why the furnace

Carbon monoxide has no smell, taste or colour, and only a CO alarm can detect it, according to Health Canada. Health Canada also lists furnaces among the sources, with the highest risk in fall and winter.

Calgary Fire puts it more directly: most commonly, the main source of CO in your home is your furnace. Its crews see more CO calls once the weather turns cold. In one November 2024 call, the cause was a vent blocked with leaves and debris that had then iced over.

Carbon monoxide detector going off with symptoms: what to watch for

Calgary Fire lists these possible symptoms of CO exposure: headaches, nausea, dizziness, confusion, fatigue, and losing consciousness.

It also lists warning signs in the house:

  • stale or stuffy air
  • a lot of moisture on windows and walls
  • soot build-up around appliances and vents
  • a pilot light that keeps going out

Any symptom, or any alarm: get out and call 911.

After a carbon monoxide detector going off: furnace, vents and alarms

Wait until the fire department, or ATCO on a gas call, tells you the house is safe to enter. Health Canada says to return only after a professional has fixed the problem. After that:

  • have a qualified technician check your fuel-burning appliances before you rely on them, even if the furnace runs again
  • keep the vents for the furnace, dryer and fireplace clear of snow and debris
  • put a CO alarm on every level, including the basement, with the most important one in or near the bedrooms (Calgary Fire)

The National Building Code of Canada calls for CO alarms near bedrooms in homes with a fuel-burning appliance. The City of Calgary recommends an electric-powered alarm with a battery back-up, and notes that most CO detectors need replacing every two to five years.

Carbon monoxide detector going off: when to send a request

Only once you're safe, and only after the fire department or ATCO says you can go back in. Then you can call or send a request for a furnace check. A local furnace technician will call you back as soon as possible. If this can't wait, call other furnace technicians too.

Questions

My carbon monoxide detector is going off. What do I do?

Get everyone out of the building now. Don't stop to open windows, look for the leak or grab things. Once you're outside, call 911. Treat a CO alarm as real, even if everyone feels fine.

Who do you call when a carbon monoxide detector is going off?

911, from outside. If you also smell gas, call ATCO's gas emergency line at 1-800-511-3447 once you're out. Don't call this website's number for a CO alarm. A furnace technician comes later, after the fire department says the house is safe.

My carbon monoxide detector went off and then stopped. Is it safe?

Don't take the silence as the all-clear. Carbon monoxide has no smell, taste or colour, so how you feel can't tell you. Get out, call 911 from outside, and wait for the fire department. Health Canada's rule is to go back only after a professional has fixed the problem.

Why is the carbon monoxide detector going off near the furnace?

Calgary Fire names the furnace as the most common source of CO in a home. That's a reason to leave, so don't stay to inspect it. Get out and call 911. Once the fire department or ATCO has cleared the house, have a professional look at the furnace.

Is it a carbon monoxide alarm or a low battery?

Don't stay inside to work it out. Treat the alarm as real: get everyone out and call 911 from outside. CO gives you no smell or colour to go on, so let the fire department check the house.

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Gas smell or CO alarm? Get out. Call 911.Site number: 587-880-3103