A burning dust smell when the furnace first starts after a long off period.

Safety first: If you smell burning plastic, electrical, or see smoke, shut the furnace off immediately. A light dusty odor at first seasonal startup is usually normal.

• Run furnace with windows cracked: Allow the furnace to run for 15–30 minutes with a few windows slightly open to clear the odor.
• Replace filter: Install a clean filter to capture additional dust.
• Inspect for abnormal signs: Remove the burner door and look for melted wiring, scorch marks, or heavy soot. If present, shut down and call a professional.

If the burning smell persists beyond the first few cycles, have the furnace inspected.