Carbon Monoxide Safety in Attached Garages: A Canadian Homeowner's Guide for 2026

Why Your Garage Door Belongs in a Conversation About Carbon Monoxide

Most homeowners think of their garage door as a piece of curb appeal or a security barrier. It is also something else: it is the air boundary between vehicle exhaust and the inside of the home. On an attached garage, almost every breath of air that ends up inside the garage eventually has to go somewhere. Some of it leaks out through the perimeter of the garage door. Some of it leaks into the house through the door to the mudroom, through the ceiling drywall, around the electrical boxes, and along the rim joist above. That second pathway is the one that kills people.

Carbon monoxide (CO) is the gas you cannot see, smell, or taste. The Government of Ontario calls it the silent killer for a reason. Over 65% of CO-related injuries and deaths in Ontario happen in the home, and an attached garage is one of the most common pathways for it to get there, as documented on the official Ontario carbon monoxide safety page. This guide walks through what CO is, why an attached garage is a particular risk, the 2026 Ontario Fire Code rules every London homeowner needs to know about, the eight habits that keep CO out of your living space, and a short note on where a smart Wi-Fi opener fits in. Every external link in this article has been checked and points to a live, official source.

None of this content is legal or medical advice. If you suspect a CO leak in your home right now, leave the building immediately and call 9-1-1 from outside. The rest of this article is meant to be read with a coffee in hand, on a quiet weekend, when you have the time to make a few small changes that may matter a lot one winter night.

What Carbon Monoxide Is and How It Gets Made

Carbon monoxide is produced any time a fuel does not burn completely. Health Canada's public infographic lists the everyday sources Canadians actually encounter at home: heating appliances such as a furnace, fireplaces and wood or pellet stoves, fuel-powered vehicles, cooking and household appliances (gas stove, gas dryer), camping stoves and barbecues, fuel-powered generators, fuel-powered equipment like lawnmowers and snowblowers, and cigarettes. The infographic is available on the Health Canada website as Infographic: Carbon monoxide.

For the purposes of an attached garage, the dominant CO source is almost always the vehicle. A modern gasoline engine produces CO every second it is running. Catalytic converters reduce CO output dramatically once they reach operating temperature, but in the first thirty to ninety seconds of a cold start (and especially in a Canadian winter), CO output can be many times higher than the steady-state number on the emissions sticker. That means a car warming up for a couple of minutes in a closed garage is, briefly, a small CO factory.

Other CO sources commonly found in attached garages include propane- or kerosene-fired space heaters, gas-powered snowblowers and lawn equipment, charcoal barbecues stored after use, and portable generators run during power outages. Each of these is covered explicitly in Health Canada's guidance on preventing carbon monoxide exposure.

What CO does to the body

CO binds to the haemoglobin in red blood cells far more tightly than oxygen does. Once enough of your haemoglobin is carrying CO instead of oxygen, your tissues start to suffocate even though you appear to be breathing normally. The U.S. Consumer Product Safety Commission's Carbon Monoxide Fact Sheet describes the early symptoms as flu-like: headache, fatigue, shortness of breath, nausea, dizziness. The CPSC notes that for slowly developing residential CO problems, occupants and physicians can mistake mild to moderate CO poisoning for the flu, which sometimes results in tragic deaths.

The CPSC's reference numbers for residential CO levels are widely cited. Most people will not experience any symptoms from prolonged exposure at roughly 1 to 70 parts per million (ppm); above 70 ppm, symptoms become more noticeable; at sustained concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible. The exact thresholds depend on individual health, length of exposure, and other factors, but the trend is clear: small concentrations matter, and the only way to know is a working CO alarm.

Why Attached Garages Are a Particular Risk

A detached garage is a relatively safe place to idle a car for a few seconds because the building envelope of the house does not share air with it. An attached garage is the opposite. The garage and the living space share a wall, a ceiling, and (almost always) a single door between them. No matter how well that wall is sealed, the pressure differences inside a Canadian house in winter (driven by the furnace, range hood, bathroom fans, and the natural stack effect) actively pull air from the garage into the house. The Ontario page is direct about it: never run a vehicle, fueled engine or motor inside a garage, even if the garage door is open. Always remove a vehicle from inside the garage immediately after starting it.

It is worth pausing on that sentence: even if the garage door is open. Many homeowners (and some online forums) believe that opening the garage door makes idling safe. It does not. CO mixes readily with air rather than streaming neatly out an open doorway, and an open door does nothing about the air the furnace is already pulling out of the garage and into the cold-air return. The garage door reduces the risk; it does not eliminate it. Health Canada's preventing-exposure page lists "do not idle vehicles in the garage, even when the garage door is open" as one of its core "keep CO out" rules.

The remote-start and keyless-ignition problem

The decade-old shift to keyless ignition and factory remote start has changed the homeowner risk profile. With a push-button start and a near-silent modern engine, it is much easier to walk away from a running car than it used to be. The U.S. National Highway Traffic Safety Administration was directed by the Infrastructure Investment and Jobs Act of 2021 to write a federal rule on automatic engine shut-off for keyless ignition vehicles, in direct response to a documented pattern of CO poisonings caused by cars left running. The lesson for Ontario homeowners is straightforward: the human in the driver's seat is now the only thing standing between a quiet, idling car and a garage filling with CO. Build the habit of physically confirming the engine is off before you walk into the house.

Remote-start systems are a related issue. Pre-warming a vehicle on a cold London morning is a comfort feature most of us appreciate, but the vehicle should never be remote-started while it is still inside an attached garage. Most factory remote-start systems will not engage if the door between the house and the garage is closed and the vehicle is in park, but the practical safety rule is simpler: pull the car out into the driveway before you remote-start anything.

The Ontario Fire Code Rules: What 2026 Changed

Ontario's carbon monoxide alarm law has its roots in the Hawkins Gignac Act, named for the Hawkins family of Woodstock, Ontario, who were killed by CO poisoning in their home. The Act, formally proclaimed by Bill 77 in 2013 and documented on the Legislative Assembly of Ontario's page for Bill 77, amended the Fire Protection and Prevention Act to give the province authority to mandate CO alarms in residential buildings.

The Hawkins Gignac framework has been in place for over a decade. What changed in 2026 was the Ontario Fire Code itself. As of January 1, 2026, the Fire Code requires CO alarms in any home that has a fuel-burning appliance, a fireplace, an attached garage, or is heated by air from a fuel-burning appliance located outside the home. The Technical Standards and Safety Authority confirms the new rules in its public notice on changes to the Ontario Fire Code: alarms must be installed adjacent to each sleeping area, and (new for 2026) on every storey of the home, including storeys without a sleeping area.

Translated for a typical London homeowner with an attached garage and a two-storey house:

• A CO alarm in the hallway outside the upstairs bedrooms.
• A CO alarm on the main floor.
• A CO alarm in the basement.
• The interior wall of the mudroom or hallway adjacent to the door from the garage is a sensible spot for one of those alarms.

It is against Ontario law to remove the batteries from a required CO alarm or to tamper with one. Landlords must install and maintain alarms in their rental units; tenants must report any issue with a unit they live in.

Choosing the right alarm

Ontario's page is explicit that CO alarms can be hardwired, battery-operated, or plug-in devices, and that combined smoke-and-CO units are acceptable. The province directs buyers to look for the logo of a recognized standards body: Canadian Standards Association (CSA), Underwriters Laboratories of Canada (ULC), or Electrical Testing Laboratories (ETL). Health Canada's buying advice is the same: buy a unit certified to Canadian standards and look for the certification mark on both the alarm and the packaging.

The CSA standard for residential CO alarms is CSA 6.19-17 (R2022): Residential carbon monoxide alarming devices. The standard's scope explicitly includes attached garages as one of the unconditioned areas these alarms are designed to protect against. A digital readout is a worthwhile upgrade over an alarm-only unit because it lets you see low background concentrations (under 30 ppm) that would not trigger the alarm but might indicate a slow leak worth investigating before it gets serious.

What NOT to Install in the Garage Itself

A CO alarm rated for residential use can be installed near (not inside) the garage. The garage itself is a temperature-extreme, dusty, exhaust-rich environment that is hard on most residential electronics. Health Canada and CSA both target the alarms at indoor living spaces. The right placement for an alarm meant to catch CO migrating from the garage is the interior side of the wall: in the mudroom, in the hallway just inside the door, or at the head of the bedroom hallway one floor up. If you also want monitoring inside the garage itself for any reason (you store equipment that burns fuel, you do woodworking in the garage), a workshop-rated CO detector with a higher dust and temperature tolerance is the correct purchase, not a household alarm.

The Eight Habits That Keep CO Out of Your Home

Hardware is half the answer. The other half is a small set of habits any household can adopt. Every item below is drawn from the published guidance of either Health Canada, the Government of Ontario, or the U.S. CPSC.

1. Never idle a vehicle in the garage, even with the door open

Start the car, open the garage door, and drive out. If you need to scrape the windshield or warm the seats, do it after the car is in the driveway. This is rule one and it is non-negotiable.

2. Confirm the engine is off before walking inside

Keyless ignition makes "did I turn it off?" a real question. Build a habit: hand on the start button, look at the dash, confirm the engine is off, then close the door.

3. Never remote-start a vehicle while it is inside the garage

Pull it out first. The convenience of pre-warming a car is real; the risk of doing it inside an attached garage is not worth it.

4. Never run gas-powered tools, generators, or barbecues in the garage

Health Canada is explicit: never run or turn on gas-powered equipment in the garage or shed. This includes lawnmowers, snowblowers, and trimmers. Operate fuel-powered generators at least 6 metres (20 feet) from any home or building. Keep charcoal and gas barbecues outside, well away from doors and windows.

5. Keep the door from the garage to the house tightly weatherstripped

The interior door is your first line of defence. Replace worn weatherstripping. Install a solid-core, self-closing door (Ontario Building Code already requires this on most new attached garages). A door with daylight visible around the frame is doing nothing to slow CO migration.

6. Maintain a tight perimeter on the garage door itself

The bottom seal, jamb seals, and threshold seal on your garage door do more than keep snow out. They reduce the volume of air swapping between the garage and the outside, which gives the rest of your sealing strategy room to work. Our guides on the bottom seal, jamb seals, and threshold seal walk through each one. A well-sealed garage is also a more comfortable garage in winter and a more efficient one, as our R-value guide explains.

7. Service fuel-burning appliances annually

Furnaces, water heaters, and gas fireplaces should be inspected once a year by a qualified contractor. In Ontario, the TSSA-registered fuels contractor directory at cosafety.ca is the place to find one. A blocked furnace vent or a cracked heat exchanger is one of the other leading residential CO sources, and the inspection is cheap insurance.

8. Test your CO alarms monthly and replace them on schedule

Press the test button on each alarm once a month. Replace the batteries on the manufacturer's schedule (most are annual). Replace the alarm itself when it reaches its end-of-life date, which is typically printed on the back of the unit and is usually seven to ten years from manufacture.

Where the Garage Door Comes In

The garage door does three things in a CO-safety conversation. None of them are dramatic; together they matter.

It is the fastest available ventilation path

If you suspect CO in the garage (you notice exhaust smell, you remembered the snowblower was running, the alarm is sounding), opening the garage door is the fastest way to move large volumes of fresh air through the space. That is the role of the door in an emergency. It is not the role of the door in routine use, where the answer is "do not run the engine in the garage at all," not "open the door first."

Its perimeter seals reduce air mixing

A well-sealed door, well-fit jamb seals, and a properly bonded threshold seal slow the exchange of air between the garage and the outdoors. That is what lets a closed house-to-garage door, a tight wall, and a working CO alarm do their jobs. A leaky garage door fights the rest of your system. Our condensation guide covers the related humidity problem; the same principle applies here.

A smart opener lets you verify the door from anywhere

The single most common "did I leave the garage open?" worry has a real safety dimension when CO is in the mix. A modern Wi-Fi-enabled opener like the LiftMaster/Chamberlain myQ-equipped models lets you check the door status and close it remotely from a phone. If you ever stand on a sidewalk fifteen minutes from home and realize you cannot remember whether you closed the door (or worse, whether the car is still running because of an unintended remote start), being able to verify the door state and the running state remotely is real peace of mind. Our smart home integration guide covers the major platforms; our Wi-Fi opener overview covers the basics; and our battery backup guide covers why the opener needs to keep working through a power outage, when generator misuse becomes a parallel CO risk.

None of these features replace good habits. They are belt-and-suspenders, not a substitute for the habits in the eight-item list above.

Power Outages: A Compounding Risk

The May 2025 ice storms left more than a million Ontario households without power for days, and they put a spotlight on the way Canadians use generators. Health Canada's rules for generator safety are unambiguous: never operate a generator indoors. Operate it at least 6 metres (20 feet) from buildings, with the exhaust directed away from open windows and doors. Keep people and pets away from it while it is running. The same rule applies to barbecues, camping stoves, and any other fuel-burning device. Every winter in Ontario produces a handful of CO incidents traceable to a generator run too close to (or, terribly, inside) a garage.

One quiet feature of modern openers is the rechargeable battery backup. With a UL 325-compliant battery-backed opener, you can still open and close the door normally for up to twenty-four hours after the power fails, which means you do not need to climb a ladder in the dark to pull the manual release. That is one fewer reason to be tempted to run a generator in a sheltered spot like a garage. Our manual release guide walks through the safe procedure if you do find yourself without battery backup during an outage.

If Your CO Alarm Sounds: What to Do

Both Health Canada and the Government of Ontario give a clear, identical playbook for a sounding CO alarm, and the steps are worth memorising:

1. Leave the home immediately. Get everyone out, including pets.
2. Do not stop to try to find the source of the CO.
3. Once you are outside, call 9-1-1 or your local fire department.
4. Do not re-enter the home until the fire department or a qualified professional has cleared it.
5. Once the source has been identified and fixed, have any affected fuel-burning appliance professionally inspected before it is used again.

If anyone is showing symptoms (headache, nausea, confusion, drowsiness), call emergency services and tell them you suspect CO poisoning. Symptoms can return when CO-laden blood is re-oxygenated, so medical follow-up matters even after fresh air seems to have resolved the immediate feeling.

Mistakes Homeowners Commonly Make

Believing an open garage door makes idling safe

Already covered above, but worth repeating because it is the single most common misconception we hear from London homeowners. The Ontario page is unambiguous: never run a vehicle inside a garage, even with the garage door open.

Using a CO alarm rated only for indoor living spaces inside the garage

Residential CO alarms are designed for interior wall mounting in conditioned spaces. Garage installation exposes them to extreme heat and cold, dust, and routine exhaust fumes that may shorten their life or cause false alarms. Mount the alarm on the inside of the house-to-garage wall, not inside the garage itself.

Skipping the annual furnace and water heater inspection

The most insidious residential CO incidents are not the dramatic "car running in the garage" kind. They are the slow, multi-week leaks from a failing furnace or cracked vent. The TSSA-registered contractor directory is the easiest way to find a qualified inspector in Ontario.

Forgetting the alarm has an end-of-life

A CO alarm is a chemical sensor and it wears out. The replacement date is on the back of the unit. After that date the sensor may stop responding to CO before it stops chirping. Replace alarms on schedule.

Running a portable generator in the garage during a power outage

This is the one mistake that kills entire families in a single night, and every winter brings new headlines. Health Canada is explicit: never operate a generator indoors, including in your garage or shed. Six metres (20 feet) from the home, exhaust pointed away from doors and windows.

Frequently Asked Questions

Does my attached garage really require a CO alarm in Ontario?

Yes. Under the Ontario Fire Code (O. Reg. 213/07) as amended for January 1, 2026, any home with an attached garage requires CO alarms adjacent to each sleeping area and on every storey, including storeys without a sleeping area. The Ontario.ca carbon monoxide safety page is the official source.

Is it safe to warm up my car in the garage if the door is fully open?

No. The Government of Ontario's explicit guidance is to never run a vehicle inside the garage even with the door open, and to always remove the vehicle from the garage immediately after starting it. Pre-warming should happen in the driveway.

Can I install a CO alarm inside the garage to catch problems early?

Standard residential CO alarms are not designed for garage conditions. If you want detection inside the garage itself, buy a workshop-rated detector. The required-by-code residential alarms belong on the interior side of the wall, in the hallway or mudroom.

I have a fully electric vehicle. Do I still need to worry about CO?

The vehicle itself is not a CO source, which is a real safety advantage. The other CO sources in an attached garage (a gas furnace in the basement on the other side of the wall, a gas water heater in the utility room, an attached workshop with stored fuel equipment, a backup propane heater) all still apply. The Ontario Fire Code rules about alarms are unchanged regardless of vehicle type.

Where exactly should I mount the alarm closest to the garage?

Follow the manufacturer's instructions, which usually specify a wall location 1.5 to 1.8 metres (5 to 6 feet) above the floor, on an interior wall, away from supply vents and exhaust fans. The wall between the garage and the house, on the interior side, is a sensible choice for one of your required-by-code alarms.

How often should I test the alarm?

Once a month. The test button confirms the circuitry and the speaker. It does not confirm the chemical sensor; for that, follow the manufacturer's replacement schedule, which is typically seven to ten years.

If I have a smart Wi-Fi opener, can I rely on it to alert me?

A Wi-Fi opener like a myQ-equipped LiftMaster or Chamberlain can tell you whether the door is open or closed and let you close it remotely. It cannot measure CO. The opener is a useful supplement; the required protection is the certified CO alarm.

What is the difference between a CO alarm and a smoke alarm?

They detect different hazards. A smoke alarm reacts to airborne particles from combustion (a fire). A CO alarm reacts to a specific gas (CO). The two alarms have different sounds, both of which every member of the household should be able to recognize. Combined units are permitted under the Ontario Fire Code and are a tidy solution for many homes, but they must still be installed in the locations required by code.

If I store my snowblower, lawnmower, and a small generator in the garage, am I at higher risk?

Storage is fine. Operation inside the garage is the problem. Move the equipment outside before you start it, every time. Health Canada is explicit on this point.

Conclusion

Carbon monoxide is one of the few household hazards that gives you no sensory warning. It is also one of the few household hazards where the protective measures are inexpensive, well understood, and largely habitual. A certified CO alarm in every required location, a tight house-to-garage door, a well-sealed garage door, and the one-line habit "never run an engine in the garage" together close the vast majority of the risk for a typical Ontario home.

If you are looking at your garage door this week and noticing that the bottom seal is brittle, that daylight is showing around the perimeter, or that the door from the mudroom to the garage no longer self-closes properly, those are good problems to fix. We can help with the garage-door side of that equation. If you would like a free quote on a new insulated door, a perimeter seal package, or a Wi-Fi-equipped opener with battery backup, call our London team at 519-619-7901, send a message through our contact page, or browse new doors and openers on our price estimator. AA Advantage Doors has been serving London-area homes since 2009; our service record is on our BBB profile.

For the official Canadian resources cited throughout this article, the best starting points are the Government of Ontario's carbon monoxide safety page, Health Canada's preventing exposure page, and the TSSA's public-safety hub at cosafety.ca. Print one, pin it to the inside of the utility-room door, and treat it as part of the home.