What belongs on a furnace maintenance checklist?
Updated August 2026
Keeping a furnace healthy comes down to a filter every 30 to 90 days, one $80–200 pro tune-up each fall, and a yearly flame-sensor cleaning and heat-exchanger inspection. The heat-exchanger check is the one that matters most: a cracked exchanger can leak carbon monoxide into the house, so it is a safety item, not just an efficiency one. Done on schedule, a furnace runs its 15 to 20 years and lights on the first cold night.
| Task | Interval | Effort |
|---|---|---|
| Check the filter, change when gray | 30–90 days | 2 min · DIY |
| Keep supply and return vents unblocked | Monthly | 5 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Test-run the furnace on a cool day | Yearly | 10 min · DIY |
| Clean the flame sensor | Yearly | 20 min · DIY |
| Vacuum the burner compartment | Yearly | 15 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Inspect the heat exchanger for cracks | Yearly | $80–200 pro |
| Check gas pressure, ignition, and venting | Yearly | incl. in tune-up |
What neglect costs
A neglected flame sensor is the most common winter no-heat call: it gets coated, stops sensing the flame, and shuts the burner down for safety, a $150–300 visit for a part you could have wiped clean. Let the filter clog and the heat exchanger overheats and cycles, which shortens its life. The expensive failure is a cracked heat exchanger: repair or replacement runs $1,500 and up, and on an older furnace it usually means buying a new one. It can also leak carbon monoxide, which is why the annual inspection is non-negotiable.
Leave these to a pro
The fall tune-up ($80–200) buys you a heat-exchanger inspection, a gas-pressure and combustion check, and a draft test on the flue, none of which you can do safely without the tools. Anything involving the gas valve, the burners, or the exchanger belongs to a licensed tech. You can absolutely handle the filter and a flame-sensor wipe yourself; leave the combustion side to the pro, and pair the visit with a working CO detector on each level.
This whole checklist ships as reminders in OnOtto: every task above, on the right schedule for your home, snooze-proof.
Load this checklist as remindersFrequently asked questions
How do I clean a furnace flame sensor?
Shut off power and gas, pull the single sensor rod near the burners (usually one screw), and gently buff the metal with fine steel wool or an emery cloth until it is shiny, then reseat it. The film that builds up is what makes a furnace light and then quit after a few seconds. It takes about 20 minutes and no parts, and it resolves a large share of mid-winter no-heat calls.
How often should I change my furnace filter?
Every 30 days for a basic 1-inch filter, stretching to 60 or 90 days for a thick pleated one, and more often with shedding pets or heavy heating use. Hold it up to the light: if you cannot see through it, change it. A clogged filter starves the blower, overheats the exchanger, and drives the 5 to 15% efficiency penalty the Department of Energy flags for dirty filters.
How do I know if my heat exchanger is cracked?
Warning signs include a flickering or yellow burner flame that should be steady and blue, soot around the furnace, a strong chemical smell, and CO detectors going off. You often cannot spot a hairline crack yourself, which is why a technician inspects it each fall. Treat it as urgent: shut the furnace off and ventilate if you suspect a leak, because a cracked exchanger can put carbon monoxide into your air.
Should I get a furnace tune-up every year?
Yes, ideally in early fall before the first hard freeze so any parts issue surfaces before you are relying on heat. The $80 to $200 visit catches a cracked exchanger, verifies safe combustion and venting, and keeps the warranty valid, since most makers require documented annual service. If your furnace is past 15 years and needs a pricey repair, weigh it against replacing the unit.