Is your furnace a carbon monoxide risk?
Carbon monoxide (CO) is a colourless, odourless gas produced when fuel burns without enough air, and a faulty gas, oil or propane furnace can release it into the house. Working CO alarms, a yearly inspection by a licensed technician and clear vents are the core of furnace safety.
How does a furnace produce carbon monoxide?
Every fuel-burning furnace makes some CO. In a healthy system the gas travels up the flue or vent and leaves the building. Trouble starts when something breaks that path or starves the flame of air. A cracked heat exchanger, a blocked flue, a failed draft or a vent outlet buried in snow can all send combustion gases back into the living space.
Because the gas has no smell or colour, people usually find out from the symptoms or from an alarm, not from the furnace. That is why CO safety is a detection and inspection problem rather than something you can judge by eye.
What are the warning signs of CO poisoning?
Early symptoms look like the flu without the fever: headache, dizziness, nausea, tiredness and confusion. Two clues point to the house rather than a virus. Everyone at home feels worse indoors and better outside, and symptoms return in the same rooms, often when the furnace has been running for hours.
Signs on the equipment deserve attention too:
- Soot, scorch marks or rust streaks around the furnace or vent pipe.
- A yellow or flickering burner flame where it is normally steady and blue.
- Condensation on windows that is new and unexplained.
- A pilot light that keeps going out.
None of these proves a leak, and a house can leak with none of them present. Treat them as a reason to book an inspection, and treat any alarm as an emergency.
Where should a carbon monoxide detector go?
Place a carbon monoxide detector outside each sleeping area and on every level, including the basement near the furnace room, following the instructions on the package. Many provincial building and fire codes require alarms in homes with fuel-burning appliances or an attached garage, so check your provincial rules and your insurer's expectations if you are unsure.
Alarms wear out. Each unit has a replacement date printed on it, and plug-in or battery models need regular testing. Replace it instead of silencing it and carrying on.
How often should a furnace be inspected for safety?
Once a year, before the heating season, by a licensed gas or oil technician, to protect your family and the home. A proper visit checks the burner, the heat exchanger, the venting and the combustion air supply, and tests for CO at the vent. Our guide to what a furnace tune-up includes lists the steps so you know what you are paying for.
Between visits, keep the area around the furnace clear, replace the filter on schedule and clear snow and ice away from outdoor vent and intake terminals after storms. High-efficiency furnaces often vent through a side wall near the ground, which makes them easy to block by accident.
Tight houses add one more factor. A well-sealed home with exhaust fans, a fireplace and a furnace competing for air can pull combustion gases back down a vent. A heat recovery ventilator supplies fresh air in a controlled way, and a blower door test shows how airtight the house really is.
What should you do if the alarm sounds?
Treat it as real. Get everyone out of the house into fresh air, including pets, and call 911 or the gas utility's emergency line from outside. Do not go back in to look for the cause. Responders will tell you when it is safe to return.
After a confirmed leak, the furnace should stay off until a licensed technician has found and fixed the fault. If the technician finds a cracked heat exchanger, repair is rarely sensible, and the repair or replace decision guide explains the trade-off. Our winter heating emergency guide covers how to stay warm in the meantime.
Does a different heating system change the risk?
A heat pump does not burn fuel, so it makes no CO by itself. Homes that keep a gas furnace as backup, or a gas water heater, stove or fireplace, still need alarms. The comparison in heat pump versus furnace and the guide to natural gas versus electric heating cover the other trade-offs. Planning a swap? See the furnace replacement guide.
The homes at Drake Landing were heated from a solar district loop for most of the project's life, so they had little combustion in daily use. After the project wound down, most switched to natural-gas furnaces (see the homes page), which means the same alarm and inspection routine applies there as anywhere else.
Quick answers
Can a new furnace leak carbon monoxide?
Yes, though it is less likely. Poor installation, blocked venting or a cracked part can cause a leak in any age of furnace, which is why alarms and inspections still matter.
Do I need a carbon monoxide detector without a gas furnace?
If anything in the house burns fuel, including an oil furnace, wood stove, gas fireplace or attached garage with a car, an alarm is recommended. An all-electric home with no combustion has far lower risk.
How long do carbon monoxide alarms last?
Most units last roughly five to ten years, and the exact figure is printed on the alarm. Replace it when the end-of-life signal sounds or the date passes.
Who can inspect a furnace for carbon monoxide leaks?
A licensed gas or oil technician for your province. Ask for the licence number and a written report of the readings taken.