Heating · decision guide
Repair or replace your furnace?
The short answer: repair a young furnace, replace an old one facing a big bill. If your furnace is under 10 years old and the fix is a few hundred dollars, repair almost always wins. Past 15 years with a major failure, heat exchanger, control board, blower motor, replacement usually wins the math. The gray zone in between is where an honest framework earns its keep.
Signs replacement wins
- Furnace is 15+ years old and facing a major repair
- Cracked heat exchanger or other safety failure
- Second significant repair in two heating seasons
- Gas bills climbing while comfort falls, efficiency is fading
- Repair quote is more than half the cost of a new unit
- Yellow burner flame, rust, or short-cycling on an old unit
Signs repair wins
- Furnace is under 10 years old
- The fix is minor, igniter, capacitor, flame sensor, thermostat
- First repair the unit has ever needed
- Unit is still under parts warranty
- You're planning to move within a year or two and the system is safe
How to think it through
The decision framework
Start with the 50% rule
If a repair costs more than half the price of a comparable new furnace, replacement is usually the smarter spend, you'd be putting big money into equipment that's still old everywhere else. In the St. Louis metro, installed furnace replacements typically run $4,000 to $8,000, so a $2,000+ repair on an aging unit deserves a hard look.
Weigh age against the failure
Missouri furnaces typically last 15 to 20 years with maintenance. Multiply the repair estimate by the furnace's age: past roughly $5,000 in 'age-dollars' (e.g., a $400 repair on a 14-year-old unit is $5,600), replacement deserves consideration. It's a rule of thumb, not gospel, but it keeps you from repairing your way through the last two winters of a dying unit.
Safety failures end the debate
A cracked heat exchanger can leak carbon monoxide into your home. It's one of the few failures where we'll tell you plainly: don't repair around it. The part is expensive, the labor is extensive, and the furnace around it is almost always near end of life.
Count the repairs, not just this one
Two service calls in two winters is a trend, not bad luck. Repeated repairs on an aging furnace usually cost more than the first year of financing on a new one, and you still have the old furnace.
The honest verdict
Under 10 years old with a small fix: repair. Over 15 with a major failure: replace. In between, apply the 50% rule and count recent repairs, and get the repair quoted honestly before anyone talks replacement. If a company leads with replacement for a five-year-old furnace, get a second opinion. Ours is free.
Quick answers
Frequently asked
- How long does a furnace last in Missouri?
- Typically 15 to 20 years with annual maintenance. St. Louis's swing seasons, hard summer humidity, real winter cold, work furnaces hard, so a neglected unit can fail years earlier. Our furnace lifespan guide covers the warning signs.
- Is a cracked heat exchanger always a replacement?
- Practically, yes. The repair is one of the most expensive on a furnace, it usually appears on units already near end of life, and the failure can leak carbon monoxide. We'll show you the crack on camera, you should never take that diagnosis on faith alone.
- Should I replace the AC at the same time as the furnace?
- If the AC is also past 12 to 15 years, often yes, the furnace blower moves your cooling air, matched systems perform better, and combined installs cost less than two separate projects. If the AC is young, keep it. We'll price both paths so you can compare.
Keep going
Want a straight answer for your home?
Bring us your situation, or another company's quote, and we'll tell you honestly which way the math points. Our comfort advisors don't work on commission, so the answer doesn't change based on what we'd sell.