A cracked heat exchanger is one of the most serious furnace problems possible. The heat exchanger is the metal chamber where combustion happens; when it cracks (usually from years of expansion-contraction cycles), combustion gases including carbon monoxide can leak into the air being blown through your home.
Stop Using the Furnace
If a cracked heat exchanger is confirmed or strongly suspected, the furnace must be shut down until repaired or replaced. The CO risk is real. We red-tag the unit and walk you through repair-vs-replace honestly — heat exchanger replacement is often comparable in cost to a new furnace.
Warning signs to watch for
- Yellow or flickering burner flame (should be steady blue)
- Soot accumulation around burners
- Chemical / formaldehyde smell when furnace runs
- CO detector intermittently alarming
- Family members getting headaches or feeling unwell during heating season
- Excessive moisture on windows when furnace runs
Detection methods
- Visual inspection (some cracks are visible with a borescope or mirror)
- Combustion analyzer reading abnormal CO in flue gas
- Pressure testing of the heat exchanger chamber
- Listening for “rumble” or change in flame pattern with the blower running
Most heat exchangers are covered by manufacturer warranty for 10-20 years on the part itself, but labor isn’t covered. Total cost including labor runs $1,400-$2,400+. For furnaces 12+ years old, full replacement is usually the smarter spend.
Related: Heat Exchanger, Carbon Monoxide, Furnace. See also: 24/7 emergency.
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Right Way Mechanical is a family-owned HVAC contractor serving Wheat Ridge, Arvada, west Denver, and the Colorado foothills.