Heat Exchanger
The sealed metal passage inside a gas furnace that transfers combustion heat to your home's air while keeping exhaust gases separate. A cracked heat exchanger can leak carbon monoxide and usually means the furnace is at end of life — it's the classic replace-don't-repair failure.
The longer answer
Heat exchangers fail from thermal cycling fatigue — years of heat-up and cool-down stress the metal until cracks form at welds and bends. Symptoms include unusual smells, soot around registers, or elevated CO readings during combustion analysis. Visual inspection with a camera scope is the standard diagnostic.
Replacement cost for a heat exchanger alone often approaches a new furnace install — which is why the honest advice at failure is usually 'replace the unit.' On furnaces under 10 years with a warranty-qualifying failure, the manufacturer may cover the part; labor still applies.
The Seattle angle
Heat exchanger inspections are standard scope on every Glendale tune-up — cracks are the safety finding that turns a repair call into a replacement conversation, especially on furnaces past 15 years.
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