What does a cracked heat exchanger mean and is it dangerous?

What the heat exchanger actually does

Inside a gas or oil furnace, burners fire into the heat exchanger while the blower pushes household air across its outside surface. The metal transfers heat to your air while keeping flue gases, including carbon monoxide, sealed inside and routed out the vent. Years of heating and cooling cycles fatigue that metal, and restricted airflow from chronically dirty filters accelerates the stress. When a crack or rust-through opens, the barrier between combustion gases and your breathing air is compromised.

Why this is treated as a safety emergency

Carbon monoxide is colorless and odorless, and exposure can cause headaches, dizziness, nausea, confusion, and worse. A cracked exchanger does not always leak heavily at first, but it does not heal, and the crack widens with every heating cycle. Warning signs can include a furnace flame that wavers when the blower kicks on, soot streaks inside the cabinet, unusual odors when the heat runs, or a CO alarm activation. Working carbon monoxide detectors on every level of the home are your essential backstop.

What to do if you suspect a crack

• ✓Turn the furnace off at the thermostat and leave it off
• ✓If a CO alarm is sounding or anyone feels ill, get everyone outside and call 911 from outdoors
• ✓Do not open the burner compartment or attempt any inspection of the exchanger yourself
• ✓Have a licensed heating technician inspect and camera-test the exchanger before the furnace runs again

Depending on the furnace's age, the answer may be an exchanger replacement or a new high-efficiency furnace; PJ MAC HVAC provides free installation estimates and its owner Doug is a Master HVAC Technician. Because a cracked heat exchanger is a real safety issue, PJ MAC HVAC responds to these calls 24 hours a day, 7 days a week.