How many carbon monoxide alarms does my Ontario home need?

Carbon monoxide is a gas you cannot see or smell. It comes from fuel that burns badly: a cracked heat exchanger, a blocked flue or furnace vent, a car idling in an attached garage. The first weeks of the heating season, October and November in York Region and Toronto, are when furnaces that sat all summer start up again, which is why the alarm question comes up now. The rule is in the Ontario Fire Code, Division B, section 2.16, as amended by O. Reg. 87/25.

Do I need a CO alarm on every floor in Ontario?

Yes, if the home has any fuel-burning appliance, a fireplace or an attached garage. Before 2026 the Fire Code only required an alarm next to sleeping areas. From January 1, 2026 it also requires one on every storey, including a basement and a main floor with no bedrooms. Homes heated by warm air from a fuel-burning appliance outside the unit are now covered too, which brings in many condo and apartment units.

An all-electric home with no fireplace and no attached garage does not need CO alarms under the Fire Code. Most Ontario houses are not in that group: a gas furnace or gas water heater alone puts you in.

How many carbon monoxide alarms do I need?

Count one for each storey, then add one for any sleeping area that is not already covered by the alarm on its floor. A sleeping area is a group of bedrooms off one hallway; bedrooms at opposite ends of a floor may need one each.

Where exactly should a CO alarm go?

Next to sleeping areas means in the hallway outside the bedrooms, close enough to wake people behind closed doors. On the other floors, put the alarm where people spend time and can hear it, not tucked in a closet. Follow the height and spacing in the manufacturer's instructions: CO mixes with room air, so unlike smoke alarms, many models can go on a wall or plug into an outlet.

• Keep it away from the furnace, water heater and stove by the distance the manual gives, often up to 5 metres (15 feet); a burst of CO when a burner lights can cause nuisance alarms.
• Avoid bathrooms, the space right above a kitchen stove, beside a window or exterior door, and dead-air corners.
• Do not put it in the garage. The alarm belongs in the house, on the floor next to the garage door.
• Combination smoke and CO alarms are allowed and save ceiling holes, but the unit must still sit where both rules want it.

Does it have to be hardwired?

Not in an existing home. The Fire Code accepts battery, plug-in or hardwired alarms there, as long as the alarm is certified to the Canadian standard (CSA 6.19, look for the mark on the box). Newer homes built under the Ontario Building Code have hardwired alarms, and a hardwired alarm should be replaced with a hardwired one. If you want new hardwired or interconnected alarms where there were none, that is electrical work: in Ontario only a Licensed Electrical Contractor can be hired to do it.

Who is responsible in a rental?

The landlord. Under the Fire Code the owner must install the alarms, keep them working, test them at least once a year and give tenants the manufacturer's maintenance instructions. The tenant must not disable an alarm and must tell the landlord promptly when one is missing, chirping or not working. Disabling an alarm or not installing required ones can lead to charges under the Fire Protection and Prevention Act, with fines of up to $50,000 or a year in jail for an individual and up to $500,000 for a corporation.

Why is my CO alarm chirping?

A single chirp every minute or so usually means a low battery. A chirp every 30 seconds, or END or ERR on the screen, usually means the alarm has reached its end of life and must be replaced: a new battery will not fix it, and the sensor may no longer detect CO. Most current alarms last 7 to 10 years; the manufacture or replace-by date is printed on the back. A long, loud pattern of beeps is a real alarm.

What should I do if the CO alarm goes off?

1. If anyone has a headache, nausea, dizziness, confusion or drowsiness, get everyone out at once, pets included, and call 911 from outside.
2. If nobody has symptoms, still treat it as real: open doors and windows, turn off fuel-burning appliances if you can do it on the way out, and call your local fire department or 911.
3. Do not go back in until the fire department says the air is clear.
4. Before using the furnace, water heater or fireplace again, have a gas technician find the source. Enbridge or your fuel supplier can also be called if you suspect a gas appliance.

How do I lower the risk before winter?

Have the furnace and other gas appliances checked once a year, ideally in early fall. A gas technician cleans the burners, checks the flame and the heat exchanger for cracks, and checks that the flue and vent pipes draw properly, which is where most household CO comes from. On Doyo, Furnace Maintenance is $206.50, the full price with Doyo's fee included, and the technician's TSSA gas certificate is checked before they are offered heating work. Test each CO alarm with its button once a month, and mark the replace-by date where you will see it.