Why does my furnace smell like it's burning when I first turn it on for the season?

This is one of the most common fall calls, and most of the time it's harmless: dust accumulates on the heating components during the months the furnace sits idle, and the first heating cycle burns it off, producing a smell similar to something on a stovetop. It's unpleasant but expected, and it should clear up quickly and not recur.

What's not normal: a burning-plastic or electrical smell (different and more concerning), a smell that persists well past the first cycle, or any smell resembling rotten eggs (that's a gas leak — leave the house and call your gas utility immediately, not us first). If the smell is genuinely just dusty and fades fast, you're fine; if you're unsure which kind you're smelling, that uncertainty alone is worth a call.