Should you repair or replace your furnace?
Updated August 2026
← Every repair-or-replace call
Repair a gas furnace under 10 years old for almost any fault except a cracked heat exchanger; replace one past 12–15 years when the repair passes half the price of a new furnace. Igniters, flame sensors, and control boards are the common failures, and they cost $150–1,500 to fix, a fraction of the $4,000–8,000 a new furnace runs installed. The exception overrides everything: a cracked heat exchanger can vent carbon monoxide, and on any furnace past 10 years it is a replacement, not a repair. Everything else comes down to age and the 50% rule.
The short version
Match the repair quote to the furnace's age before you commit. Through the first decade, fix igniters, flame sensors, blower motors, and gas valves without hesitation, because the furnace has a 15–20 year design life and these are ordinary wear parts. From about year 12 the 50% rule takes over, and a repair north of half a new furnace is throwing good money at a unit near the finish line. Safety trumps arithmetic in one case. If a technician finds a cracked heat exchanger, do not run the furnace: the crack lets combustion gases including carbon monoxide into your air, and on an older unit the only real fix is a new furnace.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Under 10 years, bad igniter, flame sensor, or control board | Repair | A $150–1,500 wear part on a furnace with a decade left |
| Blower motor failed, furnace under 12 years | Repair | A $300–1,200 motor is far below half a new furnace |
| Cracked heat exchanger, any furnace past 10 years | Replace | A carbon-monoxide hazard; the teardown nears a new unit anyway |
| Past 15 years, repair over half a $4,000–8,000 furnace | Replace | The 50% rule on a furnace at the end of its service life |
| Short-cycling from a dirty flame sensor, unit under 12 years | Repair | A clean or $20–80 sensor swap, not a replacement |
What each path costs
Repairs typically run $150–1,500; a replacement is $4,000–8,000 installed. A gas furnace lasts 15–20 years. Repair freely under 10 years; from year 12 the 50% rule applies, and a cracked heat exchanger past 10 years ends it. Price your own number on the home maintenance cost calculator before you commit either way.
The repair-or-replace call is easy when you know the unit's age and service history. OnOtto keeps both, plus the maintenance that delays this decision for years.
Start your home's service log, freeFrequently asked questions
Is a cracked heat exchanger always a reason to replace the furnace?
Practically always, yes. The part alone can be $500–1,500, but reaching it means pulling the furnace nearly apart, so the labor drives the total to $1,500–3,000, close to a new furnace. If the unit is under eight years the exchanger may be warranty-covered, which changes the math. Past 10 years, replace the furnace: the crack is a carbon-monoxide risk and a signal the exchanger has fatigued from years of thermal cycling. Shut the furnace off until it is repaired, and heat with electric space heaters in the meantime.
How do I know if a furnace repair is worth it before I pay?
Run two quick checks. First the age: if the furnace is past 12 of its 15–20 year life, lean toward replacement. Second the 50% rule: if the repair quote is more than half of a $4,000–8,000 new furnace, replacing is usually the better long-term spend, especially since a new unit burns less fuel. A $250 igniter on an 8-year-old furnace is an easy repair; a $1,500 board-and-motor job on an 18-year-old unit is not. Price both options on the cost calculator.
Does a furnace tune-up actually delay replacement?
It does, mostly by protecting the expensive parts. An annual service cleans the burners, checks the flame sensor, and inspects the heat exchanger for early cracking, catching small faults before they strand you on the coldest night. Clean burners and a fresh filter keep the blower and exchanger from overheating, which is what shortens their life. A furnace serviced and filter-changed on schedule routinely reaches the top of the 15–20 year range instead of quitting at 12.