Repair or Replace Your Furnace? A Simple Rule of Thumb
The short answer
Multiply the furnace's age by the repair quote. If the result is over $5,000, replacing usually makes more sense than repairing. Most furnaces last 15 to 20 years, so a major repair on a unit that old is often money spent on a system that will fail again soon.
The $5,000 rule
A common HVAC rule of thumb: furnace age in years times the repair cost. A 6-year-old furnace with a $400 repair scores 2,400, so fix it. An 18-year-old furnace with a $600 repair scores 10,800, so start pricing a replacement.
It's a starting point, not a law. A well-maintained older unit can keep going, and a cracked heat exchanger means replacement at any age because it's a carbon monoxide risk.
Signs it's time to replace
Any two of these on a furnace over 15 years old is a strong signal:
- Repair calls every heating season
- Rising gas bills without a change in use
- Uneven heat between rooms
- Yellow instead of blue burner flame
- A cracked heat exchanger or a CO detector alarm
What replacement costs
Most furnace replacements run about $2,800 to $7,500 installed, with a typical price near $4,700. If you also need cooling, price a heat pump at the same time; it can replace both the furnace and the AC.
Frequently asked questions
How long does a furnace last?
Most gas furnaces last about 15 to 20 years with regular maintenance.
Is it worth repairing a 20-year-old furnace?
Usually only for small repairs. A major repair on a 20-year-old unit often fails the age-times-cost test and buys you little time.
