Why a Cracked Heat Exchanger Is Different
Almost every article on furnace leaks reassures you that the water is just condensate — and most of the time, that's true. This is the one cause that's genuinely serious, and it deserves to be understood clearly.
The heat exchanger is the metal chamber that separates the toxic combustion gases (including carbon monoxide) from the clean air your furnace blows into your home. When it cracks — from age, metal fatigue, overheating, or corrosion — that separation is compromised. Combustion gases can mix with your household air, and carbon monoxide can enter your living space. While a cracked heat exchanger more often shows up as soot or a flame disturbance than as a puddle, it can be accompanied by moisture, which is why it belongs in any honest discussion of furnace leaks.
Carbon monoxide is colourless and odourless. That's exactly why it's dangerous, and why this article leads with safety. Furnaces in our area are serviced by our parent company, CanroHeat, at 604-359-1081.
Warning Signs of a Cracked Heat Exchanger
No single sign is definitive, but several together strongly suggest a heat exchanger problem:
A flickering or yellow burner flame that flexes or changes when the blower starts — a healthy flame is steady and blue.
Soot or black carbon residue inside the furnace or around the burner area.
A strong chemical or formaldehyde-like odour when the furnace runs.
Visible cracks, corrosion, or rust on the heat exchanger (usually only seen by a technician).
Physical symptoms in occupants — headaches, dizziness, nausea, or flu-like feelings that ease when you leave the house. Take these very seriously.
A carbon monoxide alarm sounding. Every BC home with gas appliances should have working CO alarms; if you don't, get them today.
If you notice these signs alongside any furnace moisture, do not keep running the furnace. Shut it off and arrange a professional inspection.
If You Suspect Carbon Monoxide — Act Immediately
This is the most important section. If your carbon monoxide alarm is sounding, or if multiple people in the home have headaches, dizziness, or nausea, treat it as a life-safety emergency:
1. Get everyone out of the home immediately — including pets. Don't stop to open windows or investigate.
2. From outside or a neighbour's, call for help. Call FortisBC's 24-hour emergency line at 1-800-663-9911, or call 911 if anyone is feeling unwell.
3. Do not re-enter until emergency responders or a qualified technician tell you it's safe.
4. Then call CanroHeat at 604-359-1081 so we can inspect the furnace and determine whether the heat exchanger has failed.
Never ignore a CO alarm or assume it's a false alarm. Carbon monoxide poisoning is preventable, and the few minutes it takes to leave and call could be the most important thing you do all year.
How It's Diagnosed and What Comes Next
A technician confirms a cracked heat exchanger through a combination of methods: a visual inspection with a camera and mirror, combustion analysis measuring CO levels in the flue, and sometimes a tracer or pressure test. It's not something you can reliably diagnose yourself, which is why a professional inspection matters whenever the warning signs appear.
If a crack is confirmed, the heat exchanger itself is sometimes covered under a manufacturer warranty (many carry 10–20 year coverage), but the labour to replace it is substantial. Because of that, on furnaces over 12–15 years old, replacing the entire furnace is frequently the safer and more economical choice than replacing the heat exchanger alone. We'll lay out both options honestly — including any warranty coverage and current BC rebates — so you can decide with full information.
Whatever the path, a furnace with a confirmed cracked heat exchanger should not be operated. Safety comes first.
Don't Take Chances With Your Heat Exchanger
A cracked heat exchanger is rare, but it's the one furnace problem where caution truly matters. If you have any of the warning signs — a yellow flame, soot, odd odours, unexplained headaches, or a CO alarm — get it inspected before running the furnace again.
CanroHeat provides thorough heat exchanger inspections and combustion analysis across Greater Vancouver, with prompt and emergency availability. Call 604-359-1081. And if a CO alarm is sounding right now, leave the home first and call FortisBC at 1-800-663-9911 or 911 — then call us.