During a routine maintenance service, our HVAC technician discovered a dangerously high carbon monoxide reading on a seven-year-old furnace during a high-fire combustion test. Further inspection revealed multiple holes in the unit’s heat exchanger. This is a critical issue because it means the exhaust from the burning gas, which should be safely vented outside, was instead leaking into the home’s circulating air. Ideally, a furnace’s heat exchanger should be completely sealed, directing all harmful exhaust fumes out through an exhaust vent, often connected to the home’s chimney. This incident underscores the vital importance of regular furnace inspections to prevent potentially life-threatening situations.