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Carbon Monoxide Hazards in Canadian Homes: A Buyer's Guide
Carbon monoxide does not give you a warning. You cannot see it, smell it, or taste it. The early symptoms feel exactly like the flu. By the time you realize something is wrong, you may already be in serious trouble.
For homebuyers, carbon monoxide is one of the most important hazards to understand before signing on a house. This is especially true for older homes with a furnace, water heater, or wood-burning appliance. A home inspection can catch many of the warning signs, but only if you know what to look for and what to ask your inspector.
Carbon monoxide is one of the invisible gas hazards that Canadian buyers should know about, alongside radon. Both gases are odourless and require specific testing or detection equipment to identify. This guide walks through a real inspection where Wesley identified a carbon monoxide hazard, what created it, and what every Canadian buyer should be checking before they take possession of a home.
Watch the Inspection
https://www.youtube.com/watch?v=yKHo3MLWVyA
Key Issues Found
- A fuel-burning appliance was showing signs of incomplete combustion or improper venting
- Vent piping had visible corrosion or improper slope
- Combustion air supply to the appliance was inadequate
- The home was at elevated risk of carbon monoxide entering the living space
- CO alarms were either missing, expired, or installed in the wrong locations
What Is Carbon Monoxide?
Carbon monoxide, or CO, is a colourless, odourless, tasteless gas produced when fuel does not burn completely. Common fuels that can produce CO include natural gas, propane, oil, wood, charcoal, and gasoline.
In a properly working appliance, fuel burns cleanly and combustion gases are vented outside through a chimney or vent pipe. When something interferes with that process, whether the appliance is malfunctioning or the vent is blocked, CO can build up inside the home.
CO is dangerous because it binds to hemoglobin in your blood more than 200 times more readily than oxygen. Your body essentially suffocates even while you continue to breathe. Health Canada provides detailed guidance on preventing CO exposure in Canadian homes.
Sources of Carbon Monoxide in a Canadian Home
Any fuel-burning appliance is a potential CO source. The most common sources in Canadian homes are:
- Natural gas or propane furnaces
- Hot water tanks
- Gas ranges and ovens
- Wood-burning stoves and fireplaces
- Gas fireplaces
- Attached garages where vehicles or gas equipment are used
- Generators or BBQs used near or inside the home
Vehicles idling in an attached garage are one of the most overlooked sources of CO in residential homes.
Common Inspection Findings That Elevate CO Risk
Backdrafting
Backdrafting happens when combustion gases that should go up the vent come back down into the home instead. The most common causes are tight building envelopes combined with depressurization from bath fans, range hoods, dryers, or central vacuums. When the home is depressurized, a natural-draft appliance cannot push its exhaust up the chimney, and the gases spill into the basement or mechanical room.
Improper Vent Slope
Furnace and water heater vent pipes should rise continuously from the appliance to the chimney. If the pipe sags or has flat sections, combustion gases pool and condense. This corrodes the metal and eventually causes leaks.
Disconnected or Corroded Flues
Vent pipes that are loose, separated, or rusted through allow combustion gases to escape directly into the home. This is one of the most common findings in older basements where the furnace and water heater share a chimney.
Cracked Heat Exchangers
A cracked heat exchanger lets combustion gases mix with the air being circulated through the home. This is a major hazard and usually means the furnace needs to be replaced. A related warning sign in older furnaces is flame rollout, which often appears in homes that also have CO risks.
Blocked Chimneys
Animal nests, leaves, debris, or collapsed liners can block a chimney. When that happens, combustion gases have nowhere to go and end up inside the house.
Insufficient Combustion Air
Natural-draft appliances need a steady supply of fresh air to burn fuel properly. Appliances installed in sealed closets or small mechanical rooms with no outside air supply can run starved for air, producing CO as a result.
What This Means for Homebuyers
If you are buying an older home, especially one with a forced-air furnace, natural-draft water heater, or wood-burning appliance, CO risk needs to be on your radar. Older homes can carry several life-safety concerns at once, including outdated electrical systems like knob and tube wiring. A thorough inspection catches them together.
Always book a full home inspection that includes an HVAC review. Ask your inspector to flag any visible venting concerns. For homes over 20 years old, consider having a licensed gas fitter perform a combustion analysis on the furnace and water heater.
Install CSA Group listed CO alarms on every level of the home and within five metres of every sleeping area. Replace any CO alarm older than 7 to 10 years. Service the furnace, water heater, and fireplace annually.
A home inspector identifies visible warning signs. A licensed gas fitter performs the combustion analysis. Both have a role to play in keeping your family safe.
What to Look For
Use this checklist when walking through a home:
- Is there a CO alarm on every level, including near bedrooms?
- Are the CO alarms within their manufacturer's lifespan (typically 7 to 10 years)?
- Does the furnace vent pipe slope upward toward the chimney without sags or flat sections?
- Is the vent pipe free of rust, holes, or visible separations?
- Are joints in the venting properly sealed and supported?
- Does the mechanical room have adequate combustion air, either through a vent to the outside or through openings to other parts of the home?
- Is there an attached garage? Are vehicles, generators, or BBQs ever used inside it?
- When was the furnace last serviced by a licensed technician?
- When was the chimney last cleaned and inspected?
Frequently Asked Questions
How do I know if my home has a carbon monoxide problem?
Install CSA-listed CO alarms on every level and near sleeping areas. A working alarm is the only reliable way to know if CO is building up. If you experience flu-like symptoms (headache, dizziness, nausea, confusion) that improve when you leave the house, suspect CO and get out.
What are the symptoms of carbon monoxide poisoning?
Headache, dizziness, nausea, fatigue, confusion, blurred vision, and shortness of breath. Symptoms often feel like the flu. Severe exposure can cause loss of consciousness and death.
Where should I install CO alarms in a Canadian home?
Install a CO alarm on every level of the home, including the basement, and within five metres of every sleeping area. Some provinces require alarms by law. Check your local code, but install them regardless.
How long do carbon monoxide alarms last?
CO alarms have a limited lifespan of approximately 7 to 10 years, depending on the manufacturer. Check the date on the back of the unit. Replace any alarm past its expiration date, even if it still beeps when tested.
Does a home inspector check for carbon monoxide?
A home inspector identifies visible CO risk factors during the inspection, including improper venting, corroded flues, missing alarms, and depressurization risks. A full combustion analysis requires a licensed gas fitter or HVAC technician, which is a separate service.
Should I be worried about CO from a gas stove?
Gas stoves can produce low levels of CO, especially if the burners are not properly adjusted. Use a range hood vented to the outside when cooking, and have the stove serviced periodically.
Are newer homes safer from CO than older ones?
Not necessarily. Newer homes are sealed tighter, which means depressurization can pull combustion gases out of natural-draft appliances more easily. Newer homes with high-efficiency sealed-combustion furnaces are generally safer, but any home with a wood stove, fireplace, or attached garage still needs CO alarms.
What should I do if my CO alarm goes off?
Get everyone out of the home immediately, including pets. Call 911 or your gas utility from outside. Do not re-enter until the source has been identified and corrected by a qualified professional.
Final Thoughts
Carbon monoxide is one of the most preventable hazards in any home. CSA-listed alarms cost less than a tank of gas. Annual furnace and water heater servicing catches most venting and combustion issues before they become dangerous. And a thorough home inspection flags the warning signs that buyers often miss.
When I inspect a home, I check the venting, the combustion air, the alarm placement, and the overall condition of the fuel-burning appliances. If something looks wrong, I tell you. If you need a gas fitter to dig deeper, I tell you that too. For more on the kind of issues most inspectors overlook, read Home Inspection Today: Learn What Others Miss.
I work for you, not the deal.