How long does a furnace last?
Updated August 2026
A gas furnace lasts 15–20 years, and a well-maintained one can reach 25–30. Modern high-efficiency condensing furnaces, the 90%+ AFUE units with a secondary heat exchanger and a PVC exhaust, tend to land in that 15–20 window because they carry more parts that can fail. Two things decide where yours ends up: whether it gets serviced every fall, and whether it was sized correctly. An oversized furnace short-cycles, snapping on and off dozens of times an hour, and every one of those starts wears the igniter, the blower, and the heat exchanger. A right-sized, yearly-serviced unit is the one that sees 25.
Lifespan by type and situation
| Type or situation | Typical lifespan | Why |
|---|---|---|
| Standard gas furnace (80% AFUE) | 15–20 years | The typical range for a conventional unit |
| Diligently serviced, right-sized | 25–30 years | Yearly service and correct sizing buy the extra decade |
| High-efficiency condensing (90%+ AFUE) | 15–20 years | More parts, and the secondary exchanger is a wear point |
| Electric furnace | 20–30 years | No combustion, so fewer parts corrode or crack |
| Oversized, short-cycling | Cut 3–7 years | Constant starts wear the igniter, blower, and exchanger |
| Never serviced, clogged filters | Cut 3–5 years | Restricted airflow overheats the exchanger |
Signs yours is near the end
- A yellow or flickering burner flame instead of a crisp blue one, a sign of poor combustion
- Banging, rattling, or a booming sound on ignition as the burners light late
- Rooms that no longer heat evenly, or a blower that runs far longer than it used to
- A creeping gas or electric bill at the same thermostat settings winter to winter
- Repair visits stacking up on a furnace already past 15 years
- Any trace of soot around the unit, or a carbon-monoxide detector that trips near it
How to add years
The single best habit is a fresh filter: a clogged one starves the blower for air and overheats the heat exchanger, the one part whose failure usually condemns the whole furnace. Book a pre-winter test and a professional service each fall so a tech can clean the burners, read the flame, and inspect the exchanger for cracks. Follow the furnace maintenance checklist and keep return vents unblocked so the blower breathes. If the unit is oversized it will short-cycle no matter what you do, so weigh a right-sized replacement once it passes 15 years and repairs start adding up.
What it costs to replace: plan on $4,500–8,000 installed (more for high-efficiency). Replacing on your own schedule, before it fails, is almost always cheaper than the emergency version. The home maintenance cost calculator helps you set the money aside before it comes due.
OnOtto tracks your furnace tune-ups age and service history, and warns you before end of life instead of after the flood.
Track your home's systems, free for 30 daysFrequently asked questions
Is it worth repairing a 20-year-old furnace?
Only if the fix is small. At 20 years a gas furnace has reached the end of its 15–20 year life, so any big-ticket repair, a heat exchanger, a control board, or an inducer motor at $500–1,500, is money poured into a unit that may fail again next winter. A $200 igniter or flame sensor on an otherwise healthy furnace is worth doing. But if the exchanger is cracked, replace the furnace: that part is both expensive and a carbon-monoxide hazard you cannot safely run.
Why does furnace size affect how long it lasts?
An oversized furnace heats the house fast, hits the thermostat setting, shuts off, then repeats, cycling on and off dozens of times an hour. Each start is the hardest moment for the igniter, blower, and heat exchanger, so all that short-cycling wears them out years early. It also leaves rooms unevenly heated and drives up the gas bill. A furnace sized to the actual heat loss of the home runs longer, gentler cycles, a big reason a right-sized unit reaches 25 while an oversized one struggles to hit 15.
How often should a furnace be serviced?
Once a year, ideally in early fall before the first cold snap. A yearly service has a tech clean or replace the flame sensor, check the burners and igniter, test the safety controls, and inspect the heat exchanger for cracks. It runs $100–200 and it is the main thing standing between a 15-year furnace and a 25-year one. Between visits, change the filter every 1–3 months so the blower always has the airflow it needs.