A carbon monoxide alarm is sounding in your home. This is a true life-safety emergency, not a nuisance alert. CO is odorless, colorless, and kills approximately 50 Canadians every year through home heating equipment failures. The good news: if you act in the next 60 seconds, the outcome is almost always fine. Here is exactly what to do, in the right order.
Immediate response in the next 60 seconds
- Get everyone OUT of the house. Adults, children, pets. Do not stop to grab belongings beyond shoes and coats. Open the front door and exit.
- Once outside, count heads. Make sure nobody is missing.
- Call 911 if anyone has symptoms (headache, dizziness, nausea, confusion, chest pain). The dispatcher will route fire department and paramedics. CO poisoning is treatable but requires immediate medical assessment.
- If no one has symptoms, call Enbridge Emergency at 1-866-763-5427 (24/7 gas emergency line). They dispatch a technician with calibrated CO meters who will enter your home, locate the source, and shut off the affected appliance.
- Do NOT re-enter the home for any reason until Enbridge or fire department clears it. This includes pets, valuables, or "just to check something."
- Stay outside. If outdoor weather is unsafe, sit in a vehicle with the engine OFF, or knock on a neighbour's door.
CO poisoning symptoms (in order of severity)
| Symptom level | What to watch for | Action |
|---|---|---|
| Mild | Headache, fatigue, mild nausea | Evacuate. Fresh air for 30 min. Call 811 (Telehealth) for medical guidance. |
| Moderate | Strong headache, vomiting, confusion, weakness | Evacuate. Call 911. Paramedics will check blood CO levels. |
| Severe | Loss of consciousness, seizures, irregular heartbeat | Call 911 immediately. Begin CPR if needed. Continued exposure is fatal. |
| Pets first | Pets often show symptoms before humans | A vomiting or lethargic pet is an early warning. Evacuate immediately. |
Even mild CO exposure causes lasting cognitive effects if not treated. Do not "wait it out" to see if symptoms pass. Get medical assessment whenever a CO alarm has sounded, even if it self-resets and people feel fine afterward.
Real CO source vs false alarm: what Enbridge will check
When Enbridge arrives (typical response 30 to 90 minutes across the GTA), they enter with a calibrated CO meter and test:
- Furnace heat exchanger (cracked exchanger is a top CO source, common on units 12+ years old)
- Water heater venting (blocked or disconnected flue can dump CO into utility room)
- Gas fireplace combustion and venting
- Gas stove / range (improperly tuned burner)
- Gas dryer venting
- Attached garage (running vehicle, generator, or BBQ can push CO through shared walls)
- Outdoor exhaust intake (any nearby vehicle exhaust, generator, fireplace can backflow into a fresh-air intake)
If CO is detected, Enbridge issues a Red Tag on the affected appliance, shuts off the gas supply to that appliance, and instructs you to have a TSSA-certified contractor repair or replace before reactivation.
False alarm scenarios (CO alarm sounds but no actual CO)
CO alarms expire. Most have a 5 to 10 year lifespan and the sensor degrades over time, becoming prone to false positives. False alarms happen most often from:
- End-of-life alarm (most common). Check the manufacture date on the back of the unit. If it is 7+ years old, replace it.
- Low battery (most modern units have a different chirp pattern for low battery vs CO detection - read the manual).
- Cleaning chemicals or aerosol sprays released near the alarm (some can trigger false readings briefly).
- Steam from showers or cooking reaching a wall-mounted alarm.
- Alarm wired to the wrong circuit and getting electrical interference.
Even if you SUSPECT a false alarm, still evacuate and call Enbridge to verify with a calibrated meter. Do not assume. The cost of being wrong is too high.
After Enbridge clears the source: HVAC next steps
Once Enbridge identifies the source appliance and Red Tags it, you need a TSSA-certified HVAC contractor to inspect, repair, or replace. EcoFrost handles all post-CO HVAC work across the GTA:
| Source | Typical action | Cost range |
|---|---|---|
| Cracked heat exchanger (furnace) | Heat exchanger replacement OR full furnace replacement | $1,800 to $3,200 for HX swap; $3,500 to $8,500 for replacement |
| Blocked or disconnected vent | Vent repair, may include B-vent inspection | $250 to $850 |
| Failed water heater venting | Vent replacement or full water heater swap | $350 to $2,800 |
| Mis-tuned gas valve | Recalibration and combustion test | $185 to $485 |
| Indoor air leak from attached garage | Air seal between garage and house | $185 to $650 |
EcoFrost runs a full combustion analysis on every post-CO call to confirm the repair is complete and the unit operates within safe parameters. We do not just replace the affected part and walk away.
CO alarm placement: where to put them (Ontario Fire Code 6.3.3)
Ontario fire code requires a CO alarm on every storey of your home and within 5 metres of every sleeping area. Best practice goes further:
- Outside every bedroom or sleeping area (hallway placement is fine).
- On every level of the home, including the basement.
- Within 5 metres of any fuel-burning appliance (furnace, water heater, gas fireplace, gas stove).
- NOT directly above or beside the appliance itself (CO disperses through the air, and direct mounting can produce false alarms from normal startup).
- NOT in kitchens, bathrooms, or garages (false alarm zones).
- At sleeping head-height, not floor or ceiling. CO mixes with air at all heights, so wall placement at chest level is fine.
Replace CO alarms every 7 to 10 years per manufacturer specification. Check the manufacture date stamped on the back of each unit. Combination smoke + CO alarms count, but verify the CO sensor portion has not expired separately.
Prevention: catching CO risks before the alarm sounds
Three concrete steps catch the most common CO failure modes before they put your family at risk:
- Annual professional furnace tune-up with combustion analysis. EcoFrost flat $149 includes a scoped heat exchanger inspection on every unit. We have caught dozens of cracked exchangers that homeowners had no clue about.
- Replace your CO alarms on schedule. Add a calendar reminder for year 7 of every alarm purchase. Replacement cost is $35 to $80 per unit.
- Service your water heater venting whenever you replace the water heater itself, and inspect annually if your water heater is 8+ years old.
For a deeper look at heat exchanger warning signs, read our <a href="/blog/signs-you-need-furnace-repair-gta">7 signs your furnace needs repair</a> guide.
Ready to take the next step?
Book a Combustion Safety Inspection - $149?Frequently Asked Questions
What do I do if my CO alarm goes off?
Who do I call first when my CO alarm sounds: 911 or Enbridge?
How quickly does CO poisoning happen?
Why did my CO alarm go off but Enbridge found nothing?
What appliance causes CO in homes most often?
Will my CO alarm work without batteries during a power outage?
How much does heat exchanger replacement cost in Ontario?
Can I keep using my furnace if Enbridge Red Tagged it?
EcoFrost Heating & Cooling
Toronto's Trusted HVAC Experts Since 2015
Our certified HVAC technicians have served 5,000+ Toronto-area homes. We write about heating, cooling, and air quality from real field experience not marketing copy. Learn about us →
