Component
Heat exchanger
The heat exchanger transfers combustion heat to the air while keeping flue gas separate from the house air. Condensing furnaces have a primary and a stainless secondary exchanger. Cracks and corrosion are the serious failures because they can let combustion gas into the airstream.
Carbon-monoxide alarm sounding?
- Do not operate light switches, appliances or phones inside.
- Leave the building and leave the door open behind you.
- From outside, call the FortisBC emergency line at 1-800-663-9911 or 911.
- Only after that, call BC Wide about the furnace.
A furnace that will not run is a breakdown, not a gas emergency. Gas smell, a CO alarm, soot or scorching are.
Short answer
A cracked heat exchanger is the classic reason a furnace is taken out of service: it can allow carbon monoxide into the supply air. Technicians inspect heat exchangers visually and with combustion testing during maintenance and diagnosis. If a heat exchanger is confirmed failed, the furnace is not run and replacement is the standard outcome, since the repair is usually not economical or permitted.
Two exchangers on condensing furnaces
Condensing furnaces use an aluminized-steel primary exchanger for the main heat transfer and a stainless-steel secondary exchanger that wrings out the latent heat, producing the condensate. Manufacturers publish the material and design (Carrier's product data describes both for every family documented on this site).
What kills heat exchangers
Overheating from airflow starvation or oversizing, corrosion from condensate or chlorides, and thermal stress from poor burner operation all shorten exchanger life. A furnace that has repeatedly tripped limits or run with a blocked filter is the profile for early exchanger failure.
Inspection and the CO question
Annual maintenance includes a visual inspection of the exchangers where accessible plus combustion analysis, because a developing crack may show in the combustion readings before it is visible. If carbon monoxide is detected in the supply airstream, the furnace is shut down immediately; that is a leave-and-call situation.
Related
- ServiceFurnace InspectionA documented furnace inspection for buyers, sellers, strata and insurers
- ServiceFurnace MaintenanceAnnual furnace maintenance that checks what actually fails
- ServiceGas Furnace ReplacementReplace an aging or failed furnace with the right high-efficiency furnace for your house
- SymptomFurnace overheating and limit trips
- SymptomFurnace not heating
Questions people ask
Is a cracked heat exchanger always fatal to the furnace?
In practice, yes: manufacturers do not sanction field repairs of heat exchangers, and the parts plus labour rarely make sense against replacement. A confirmed crack means the furnace is taken out of service and replaced.
What causes white residue or rust around the heat exchanger?
Condensate that is not draining properly, or chlorides from the air or cleaning products, can corrode exchanger surfaces. The pattern of the damage tells the technician which cause to address.
Do warranties cover heat exchangers?
Heat exchangers carry the longest warranties (often lifetime on registered equipment, as stated on this site's model pages). Coverage is conditioned on registration, installation and maintenance per the manufacturer's requirements.
Need this looked at?
Call BC Wide with the brand, model number and anything on the display. Or
Request service online with this page attached.