Carbon Monoxide and Your Furnace: A Calgary Homeowner Safety Guide
Quick answer: A gas furnace can leak carbon monoxide if its heat exchanger is cracked, its venting is blocked or it isn’t burning fuel properly. You can’t see or smell CO, so every Calgary home with gas appliances needs CO alarms on each level. If an alarm sounds, get everyone outside and call 911.
Carbon monoxide (CO) is the reason every Calgary HVAC technician takes furnace safety seriously. It’s a poisonous gas you can’t see, smell or taste, and in a closed-up house in January it can build up without anyone noticing. The good news is that CO problems from furnaces are almost always preventable. This guide explains how a furnace can leak CO, the symptoms to watch for, where to put your alarms, and exactly what to do if one goes off.
What Carbon Monoxide Is and Why It's Dangerous
Carbon monoxide is produced when fuels like natural gas, propane or wood don’t burn completely. Normally, a furnace burns gas cleanly and sends any combustion gases outside through its vent pipes. When something goes wrong, those gases can end up in your home instead.
CO is dangerous because it stops your blood from carrying oxygen properly. At low levels it causes headaches and tiredness; at high levels it can cause unconsciousness and death. According to Health Canada, it can only be detected with a carbon monoxide alarm.
How a Furnace Can Leak Carbon Monoxide
A cracked heat exchanger
The heat exchanger is the metal chamber that keeps burning gas separate from the air you breathe. Years of heating up and cooling down can crack it, especially in older furnaces. A crack can let combustion gases mix with the air your blower sends through the house. This is one of the main reasons technicians recommend replacing very old furnaces rather than repairing them.
Blocked or frosted vent pipes
High-efficiency furnaces vent through two white plastic pipes on an outside wall. In a Calgary winter, snow drifts, ice or even a bird’s nest can block them. Most modern furnaces have a safety switch that shuts the furnace off when the vent is blocked, but disconnected, damaged or poorly installed venting can still leak. Older mid-efficiency furnaces that vent up a chimney can be affected by a blocked or deteriorating chimney liner.
Poor combustion
Dirty burners, the wrong gas pressure or a shortage of combustion air can cause gas to burn incompletely and produce more CO. A lazy, yellow or flickering flame instead of a steady blue one is a warning sign. Storing boxes, laundry or paint cans around the furnace can starve it of the air it needs.
Other sources in the home
Your furnace isn’t the only possible source. Gas water heaters, fireplaces, gas ranges and a car left running in an attached garage can all produce CO. That’s why alarms matter even if your furnace is new.
Symptoms of Carbon Monoxide Exposure
Early symptoms are easy to mistake for the flu, except there’s usually no fever:
- headache
- nausea or vomiting
- dizziness or light-headedness
- drowsiness or unusual tiredness
- confusion or trouble thinking clearly
- shortness of breath
Be suspicious if several people in the house feel unwell at the same time, if pets seem sick too, or if symptoms ease when you leave home and return when you come back.
Where to Install CO Alarms
The City of Calgary’s carbon monoxide alarm guidance recommends at least one CO alarm on every level of your home, including the basement, with the most important location in or near the bedrooms. Health Canada says the most important place is in hallways outside sleeping areas.
- Every level: including the basement, where the furnace and water heater usually are.
- Outside bedrooms: close enough that the alarm will wake everyone. If you can’t hear it with doors closed, add alarms inside bedrooms.
- Follow the manufacturer’s instructions for height and distance from appliances. CO mixes with room air, so it doesn’t need to be on the ceiling unless it’s a combination smoke and CO alarm.
- Not in the garage, and not right next to a window, door or supply vent where fresh air can dilute the reading.
- Choose a certified alarm with battery backup, so it still works in a power outage. A digital display that shows low readings is helpful.
Testing and Replacing Your Alarms
- Press the test button once a month.
- Replace batteries at least once a year, unless the alarm has a sealed battery.
- Replace the whole alarm by the date or end-of-life warning on the unit, typically 7 to 10 years after it was made. CO sensors wear out.
- Write the install date on the alarm with a marker.
What to Do If Your CO Alarm Goes Off
- Get everyone outside right away, including pets. Don’t stop to look for the source.
- Call 911 from outside.
- Don’t go back in until emergency responders say it’s safe.
- Before using the furnace again, have a licensed technician find and fix the cause.
If anyone has symptoms, tell the 911 operator. If you smell gas (a rotten-egg smell) rather than hearing a CO alarm, leave the house and call the ATCO Gas emergency line at 1-800-511-3447 or 911 from outside.
If the alarm is chirping every 30 seconds or so rather than sounding a full alarm, it usually means a low battery or that the alarm has reached the end of its life. Check the label or manual, and replace it if it’s expired.
How a Yearly Tune-Up Protects You From CO
The City of Calgary recommends having fuel-burning appliances, chimneys and vents inspected by professionals every year before you start using them. A proper furnace tune-up includes:
- inspecting the heat exchanger for cracks and corrosion
- checking the venting for blockages, leaks and correct slope
- cleaning the burners and checking the flame
- testing gas pressure
- testing for carbon monoxide at the furnace and vents
- checking the safety switches that shut the furnace off if something goes wrong
Our Calgary furnace winter prep checklist covers the other jobs to do before the cold arrives.
Calgary Winter Risks to Watch For
- Snow-blocked vents: after every storm, check that the white intake and exhaust pipes on the side of your house are clear.
- Closed-up homes: in deep cold, windows stay shut for weeks, so any CO has nowhere to go.
- Warming up the car: never run a vehicle in an attached garage, even with the door open.
- Space heaters and generators: never use fuel-burning heaters, barbecues or generators indoors or in the garage.
- Odd furnace smells: a lingering burning smell can point to a problem. See our guide to what furnace burning smells mean.
When to Repair or Replace
If a technician finds a cracked heat exchanger, the furnace should not be used until it’s fixed, and on most older furnaces replacing the whole unit is the safer and better-value choice. For other faults, such as a dirty burner, a failed inducer motor or a damaged vent pipe, a repair is usually enough. If you’re unsure, ask for written prices for both. Purcell Heating & Air offers 24/7 furnace repair in Calgary and furnace replacement, with licensed gas fitters working under Alberta gas ticket LGA 0209624.
Frequently Asked Questions
Can a furnace leak carbon monoxide?
Yes. A gas furnace can release carbon monoxide if its heat exchanger is cracked, its venting is blocked or disconnected, or it isn’t burning fuel properly. That’s why every home with a gas furnace needs working CO alarms and a yearly professional inspection of the furnace and its venting.
What are the signs of a carbon monoxide leak?
Carbon monoxide has no colour, smell or taste, so an alarm is the only reliable warning. Symptoms in people are flu-like, without a fever: headache, nausea, dizziness, drowsiness and confusion. Signs that several people or pets feel unwell at home, and better away from it, are a red flag.
Where should CO detectors go in my home?
Install a carbon monoxide alarm on every level of your home, including the basement. The most important spot is in the hallway outside bedrooms, so the alarm wakes you. Follow the alarm maker’s instructions for height and placement, and don’t put one in the garage.
How often should I replace my CO alarm?
Replace the whole alarm by the date or end-of-life warning on the unit, typically 7 to 10 years after it was made. Test it monthly with the test button and replace batteries at least once a year. Write the install date on the alarm so you know when it’s due.
Does a furnace tune-up check for carbon monoxide?
A proper tune-up should. The technician inspects the heat exchanger for cracks, checks the venting, confirms the burners are burning cleanly, and tests for carbon monoxide at the furnace and vents. Ask for the results in writing, and keep your home’s CO alarms in place as well.