Carbon Monoxide Safety: Why GTA Homes Need an Annual Furnace Check

Every fall, a few stories make the news: a family in the GTA rushed to hospital, a pet that didn’t make it, a CO alarm that never went off because the battery had been pulled years ago. Carbon monoxide is the silent killer of home safety stories because that’s literally what it is — colourless, odourless, and a normal by-product of burning natural gas.

A modern furnace is designed to vent every bit of CO safely outside. But furnaces are mechanical equipment that runs thousands of hours a winter, and components wear. An annual professional check is the difference between catching a small issue in September and discovering it the hard way in January.

What carbon monoxide actually is — and why furnaces produce it

Carbon monoxide (CO) is a gas formed when fuels like natural gas, propane, oil, or wood burn without enough oxygen. Complete combustion produces carbon dioxide and water vapour — both harmless at the levels a furnace creates. Incomplete combustion produces CO.

A healthy gas furnace burns cleanly and vents all of those exhaust gases up the flue to the outdoors. The combustion stays sealed inside the heat exchanger, a metal chamber that warms the air being pushed through your ducts without ever letting exhaust mix with it.

The risk shows up when that separation fails. A cracked heat exchanger, a blocked vent, a clogged burner, or a starved combustion air supply can all push CO into the air your family breathes.

How CO actually hurts you

CO bonds with the hemoglobin in your blood roughly 200 times more readily than oxygen does. Even small concentrations gradually displace oxygen in your bloodstream, which is why symptoms feel like a slow flu rather than a sudden poisoning.

Children, seniors, pregnant women, and pets show symptoms at lower concentrations and faster. So does anyone with heart or lung conditions. By the time anyone realises what’s happening, judgment is already impaired — which is why detection has to be automatic.

If your CO alarm sounds, or anyone in the home shows symptoms like headache, dizziness, nausea, or confusion: get everyone (and pets) outside into fresh air immediately. From outside, call 911 and the TSSA emergency line at 1-877-682-8772. Do not go back in to open windows, turn off the furnace, or grab belongings. Wait for professionals to declare the home safe.

What an annual furnace check actually covers

A real safety inspection is more than a quick filter change. When a Delson Air technician arrives for an annual furnace check in a GTA home, the work includes:

• Heat exchanger inspection with a borescope or mirror, looking for cracks, rust-through, or warping
• Combustion analysis with a calibrated meter measuring CO, CO2, and oxygen at the flue
• Flue and vent inspection for slope, secure connections, blockages, and corrosion
• Burner cleaning and flame pattern check — a clean, steady blue flame is the goal
• Gas pressure measurement at the manifold, adjusted to manufacturer spec
• Pressure switch, limit switch, and rollout switch testing
• Condensate drain check on high-efficiency units
• Blower motor amperage draw, belt condition (where applicable), and wheel cleaning
• Thermostat operation and safety lockout sequence verification

The combustion analysis is the part that catches CO issues early. A furnace can look fine to the eye while producing levels of CO that would not yet trigger an alarm but would shorten the life of the heat exchanger and risk a future event.

When CO risk goes up

A few situations sharply raise the odds of a CO problem in a GTA home:

1. Furnaces older than 15 years, especially mid-efficiency units with steel heat exchangers
2. Vents that share with a water heater if either appliance has been replaced without rechecking the draft
3. Heavy renovations that changed airflow — new windows, basement finishing, range hoods, or HRVs can starve a furnace of combustion air
4. Blocked exterior vent terminations from snow drifts, ice, leaves, or wasp nests — extremely common in Toronto and Mississauga winters
5. A furnace that won’t stay lit, short-cycles, or behaves oddly — these symptoms overlap with a furnace not turning on properly and warrant a service call rather than a reset

Pay particular attention to the outdoor vent on the side of your house after any heavy snowfall. A buried intake or exhaust forces the furnace into incomplete combustion within minutes.

Carbon monoxide alarms — the law and the smart practice

Ontario’s Hawkins-Gignac Act requires every home with a fuel-burning appliance or an attached garage to have working CO alarms. The minimum is one alarm outside each sleeping area. That’s the floor, not the goal.

Where to place them

• Outside every sleeping area (required)
• One on every storey of the home, including the basement
• Within about 5 metres of the furnace and water heater
• Not directly above the furnace, beside a window, or in dead-air corners — follow the unit’s manual

How to maintain them

• Test monthly with the test button
• Replace batteries annually unless the unit is hardwired or has a sealed 10-year battery
• Replace the whole alarm every 7–10 years — sensors expire even when the alarm beeps normally
• Combination smoke/CO units are fine; just confirm both sensors are within their service life

A loud chirp that won’t stop usually means end of life, not a low battery. Check the date printed on the back before you assume it’s a false alarm.

Why fall is the right time to book

GTA technicians get hammered with no-heat calls from late October onward. Booking your inspection in August or September means:

• Real diagnostic time, not a rushed mid-winter visit
• Parts in stock if anything needs replacement
• Any required heat exchanger work done before the furnace runs daily
• Better appointment windows — evenings and Saturdays are still available
• Time to act on findings before cold weather forces a decision

If you’re already planning to layer in fall HVAC maintenance for your Ontario home, the furnace inspection is the centrepiece of that checklist.

When to call Delson Air

Carbon monoxide is the one HVAC issue where waiting is genuinely dangerous. If your CO alarm has sounded, your furnace is more than a decade old without a recent inspection, or anyone in the home is feeling unexplained headaches that ease when they leave the house — pick up the phone.

Delson Air serves the entire Greater Toronto Area — Toronto, Mississauga, Markham, Vaughan, Brampton, Richmond Hill, Oakville, and surrounding cities. We’re TSSA-licensed, Enbridge Authorized Contractors, and fully insured, which means every annual furnace check includes proper combustion analysis and a written report you can keep for your records and warranty.

Call (647) 467-9919 to book your annual furnace inspection, or reach out through our contact page and we’ll get back to you the same business day. Your comfort is our priority — but your safety comes first.