How often should you replace a furnace?
Updated July 2026
A gas furnace lasts 15 to 20 years, and a lightly used, well-serviced unit can stretch to 25 or even 30. The catch is that both reliability and efficiency start sliding after year 15, so anything past that is borrowed time. Plan the replacement rather than gambling on the furnace surviving one more January, because a no-heat failure has a way of happening during the coldest week, at emergency rates.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Low-use, well-serviced gas furnace | Plan at 20-25 years | Light duty and yearly tune-ups reach the top of the range |
| Average use, some maintenance | Plan at 15-18 years | The reliability curve bends down after year 15 |
| Cracked heat exchanger found | Replace now | A cracked exchanger leaks carbon monoxide and is not worth patching |
| Repair cost over half a new furnace | Replace | The 50% rule: a big fix on an old unit rarely pays off |
| 80% AFUE unit, high gas bills | Consider upgrading | A 95%+ furnace cuts fuel use and may qualify for a rebate |
| Under 12 years, common part fails | Repair | Igniters and sensors are cheap; keep a mid-life furnace running |
The cost of skipping it
Why not run it to failure: a dead furnace in a cold snap means emergency-rate service, a scramble for equipment, and the real risk of frozen, burst pipes if the house drops below freezing while you wait. A planned replacement runs $4,000-8,000 installed and lets you upgrade from an old 80% AFUE unit to a 95%+ condensing furnace that trims the gas bill. The one non-negotiable trigger is a cracked heat exchanger, which leaks carbon monoxide and ends the debate. Price the swap in the cost calculator before winter.
How to do it (Planning task · pro install $4,000-8,000)
- Find the age on the furnace label or by looking up the serial number, and once it is past 15 years, plan ahead.
- Have the heat exchanger inspected at the annual tune-up; a confirmed crack means replace, not repair.
- Measure any big repair against the 50% rule before sinking money into an old cabinet.
- Compare AFUE ratings when you shop; a 95%+ furnace can repay its premium in fuel savings.
- Book the job in spring or fall, when HVAC crews are slower and pricing is softer.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing furnace replacements schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
What are the signs a furnace is near the end?
Watch for climbing gas bills, repairs coming closer together, uneven heat between rooms, a burner flame that burns yellow instead of crisp blue, more rattling and banging on startup, and an age past 15 years. A single sign is not a death sentence, but several together mean it is time to get replacement quotes rather than pour money into the next breakdown.
Can I just keep repairing my old furnace?
Up to a point. Cheap, common parts like a $15-50 igniter or flame sensor are worth replacing on a mid-life furnace. The lines you do not cross are the 50% rule, where a repair costs more than half a new unit, and a cracked heat exchanger, which is a carbon-monoxide hazard no repair fixes safely. Past either, keeping the old furnace alive costs more than it saves.
Should I switch to a heat pump instead of a new furnace?
It is worth pricing, especially in milder climates or with a dual-fuel setup that keeps the gas furnace for the coldest nights. Heat pumps run on electricity, handle both heating and cooling, and often qualify for incentives, but the math turns on your local electric rates and winter lows. Get a contractor to quote both a straight furnace swap and a heat pump so you can compare the real numbers side by side.