Where to Put Carbon Monoxide Alarms in a Canadian Home

Does your home need a CO alarm?

Health Canada's baseline, for anywhere in Canada: if you have or use fuel-burning (combustion) appliances or equipment at home, install smoke alarms and at least one carbon monoxide alarm with battery backup.

Ontario's legal requirement (Fire Code, as updated January 1, 2026). A house needs CO alarms if it has any of:

• A fuel-burning appliance (gas or oil furnace, gas water heater, gas stove, and so on)
• A fireplace
• An attached garage
• Heat supplied as air from a fuel-burning appliance outside the home (new for 2026)

Apartments and condos need them if the unit has a fuel-burning appliance or fireplace, sits directly above, below, or beside a service room or garage, or is heated by air from a fuel-burning appliance outside the unit. From January 1, 2026, alarms are also required in public corridors heated by air from a fuel-burning appliance.

Outside Ontario, requirements come from your province's building and fire codes and your municipality, and they differ, particularly for older homes. Your local fire department can tell you what applies to your house. If you have any fuel-burning appliance or an attached garage, the safe answer is yes, whatever your province requires.

Where carbon monoxide alarms go

• Outside every sleeping area. Ontario defines this as the hallway or area just outside the bedrooms, so one alarm in the hallway nearest a group of bedrooms covers them. Health Canada names this as the single most important location, because you need to hear it while you sleep.
• On every storey. Required in Ontario since January 1, 2026, including storeys with no bedrooms. The City of Calgary recommends the same: at least one alarm on every level, including the basement.
• Follow the manual for height and clearances. CO alarms are not all mounted the same way. The manufacturer's instructions set the mounting height and how far to keep the alarm from fuel-burning appliances and other spots that cause false readings.
• Put one where you'll hear it. A bedroom hallway alarm only works if it wakes you with the doors closed. Interconnected alarms, where one sounding sets off the rest, help in larger or multi-storey homes.

Ontario's rules are in Section 2.16 of Division B of the Ontario Fire Code (O. Reg. 213/07), as amended by O. Reg. 87/25, in force January 1, 2026. For anything specific to your building, Ontario's advice is to contact your local fire department.

A worked example: a typical two-storey house

Take a two-storey Ontario house with a finished basement, a gas furnace and water heater in the basement, and an attached garage. Applying the Ontario rules above:

• Upstairs: one alarm in the hallway outside the bedrooms. If the bedrooms are split between two separate areas, each area gets one.
• Main floor: one alarm. This is the floor most people skipped before 2026, and it is now required.
• Basement: one alarm, and outside the basement bedroom if there is one.

That is at least three alarms for a house that may have had one before. Combination smoke and CO alarms can cover both jobs in the same spot, as long as you also meet your smoke alarm requirements.

Choosing an alarm

• Look for a certification mark. Health Canada says certification marks to Canadian safety standards must be on the alarm and its packaging. Ontario lists CSA, ULC, and ETL as examples of recognized testing agencies.
• Battery backup. Health Canada specifically recommends an alarm with battery backup, so a plug-in or hardwired unit keeps working in a power outage, which is exactly when people bring generators and heaters into play.
• Check the expiry date before you buy, and write the install date on the alarm.

Testing, chirping, and when to replace

• Test every alarm monthly with the test button (Ontario).
• Replace batteries yearly (Ontario), unless your model has a sealed long-life battery. The City of Calgary makes the same exception for 10-year lithium battery alarms.
• Replace the whole alarm when it expires. CO sensors wear out. Calgary notes lifespans of 5 to 10 years depending on the manufacturer; check the date on the back or the packaging.
• A chirp is not an alarm, but it is not nothing. A periodic chirp usually means a low battery or an alarm at end of life. Each manufacturer uses different patterns for low battery, end of life, and a real CO alarm, so keep the manual (or look up the model online) to tell them apart. If you can't tell, treat it as an alarm.

Our annual home safety checklist puts alarm testing on the same day as the rest of the yearly safety audit, so it actually happens.

If the CO alarm goes off

Health Canada's steps, in order:

1. Leave the home immediately and get to fresh air. Bring people and pets.
2. Don't try to find the source.
3. Once outside, call 9-1-1, your local fire department, or emergency services.
4. Go back in only after a professional has fixed the problem.

Ontario notes that people may already have symptoms when an alarm sounds. Early signs are headache, nausea, dizziness, confusion, and drowsiness; higher exposure causes loss of consciousness and death. If several people in the house, or the pets, feel unwell at the same time, especially when the furnace is running, treat it as CO until proven otherwise. Ontario also reports that over 65% of CO-related injuries and deaths in the province happen at home.

Landlords and tenants (Ontario)

• Landlords must install and maintain CO alarms in rental units, test them annually (and at certain other times), and give tenants the maintenance instructions.
• Tenants must tell the landlord about any problem with an alarm. Removing batteries or tampering with an alarm is against the law.

Keeping carbon monoxide out in winter

An alarm warns you. These habits keep it from going off in the first place:

• Have fuel-burning appliances, chimneys, and vents cleaned and inspected by a professional every year before the cold weather (Ontario).
• Keep outside vents and chimneys clear of snow. On a high-efficiency furnace the vents are usually plastic pipes low on an outside wall; our winter home prep guide covers finding and clearing them.
• Don't idle a vehicle in the garage, even with the garage door open, and keep the door between the house and the garage closed (Health Canada).
• Run a generator outdoors only, at least 6 metres (20 feet) from any building (Health Canada), and never in the garage or shed. Barbecues stay outdoors too. Our power outage gear guide covers ways to keep warm and lit without a fuel-burning heater.
• Never use a stove or oven to heat the house (Ontario).