Turning On the Heat for the First Time This Season? Do This First

The worst night to discover a furnace problem is the first cold one — when every repair shop's phone is ringing and the earliest slot is Thursday. Ten minutes on a mild afternoon beats that whole experience.

Safety first, every page: if you smell gas — rotten eggs — at any point, leave the house and call your gas company from outside.

The ten-minute pre-season checklist

1. New filter in. A furnace should start its season breathing clean. Hold the old one to a light for the verdict, but after a summer of AC duty, just replace it. Note the size and date on the frame's edge.
2. Vents open, returns clear. Walk the house: supply vents open, nothing parked against the big return grilles. Summer furniture rearranging loves to block a return.
3. Three feet clear around the furnace. Whatever migrated next to it over the summer — boxes, paint cans, the beach chairs — moves now. Paint, gas cans, and solvents don't live near a furnace, ever.
4. Check the outdoor vent pipes (high-efficiency furnaces: the white PVC pipes outside). Clear leaves, nests, and debris from the openings. In winter, snow; in fall, everything else.
5. Thermostat: fresh batteries, HEAT mode, fan on AUTO. Set it 3–4 degrees above room temperature for the test.

The test run — on a mild day, on purpose

Let it run 15–20 minutes. Here's what's normal and what's not:

• A dusty burning smell, house-wide, fading within the hour — normal. That's summer's dust cooking off the burners. Crack a window, let it finish. A smell that's still there tomorrow, or smells like burning plastic, is not that — see the burning smell page.
• Warm air within a few minutes at every vent — normal. Weak flow at some vents: check those rooms' vents and dampers.
• A bang at startup, repeated cycling on-off, clicking without heat — not normal. Not an emergency on a mild day, which is the whole point: you just found out while it's 60° out and the repair calendar is empty.

Why the mild-day timing is the actual trick

The first cold snap is the biggest furnace-failure day of the year, and every failure books a truck. Test two weeks early and you're either confirmed-ready, or you're scheduling a repair in the quiet week at normal prices. That's the entire strategy. It costs ten minutes.

Related symptoms

• Burning smell when the heat first comes on
• Furnace won't turn on
• How often to change the furnace filter

Start the free troubleshooter → Free, no sign-up. If the test run turns up anything odd, it walks you through what a tech would check next.

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