Quick answer
Repair a young furnace with a cheap, isolated fault; replace an old one facing a major component failure. In between, weigh three things: age against ENERGY STAR's 15-year furnace guideline, the repair quote against the equipment's remaining value, and whether this is the first failure or the third this winter. A cracked heat exchanger is the exception — that's a replacement conversation, full stop.
- ENERGY STAR's guideline: consider replacement when a furnace is more than 15 years old.
- Weigh repair cost against remaining life — a big repair on an old furnace buys the least time per dollar.
- Repeat breakdowns are data: the third repair in two winters usually signals the end.
- A cracked heat exchanger is a safety issue, not a repair-vs-replace debate.
- Replacement is also the moment to fix sizing and duct problems the old system hid.
When is repairing the furnace clearly the right call?
Age is the anchor. A furnace under 10 years old with an isolated failure — an igniter, a flame sensor, a blower capacitor, a pressure switch — is almost always a repair. These are consumable-grade parts, the fix is inexpensive relative to replacement, and the furnace has years of design life left. Gas furnaces routinely serve 15–20 years when maintained, so a young furnace's first breakdown is an event, not a verdict.
The pattern matters more than the incident: one failure in a decade is normal wear. If the same furnace has needed a technician every winter, each individual repair may look cheap while the trendline says otherwise — that's the machine telling you where it's headed.
When does replacement become the smarter money?
ENERGY STAR's guidance puts the consideration threshold at more than 15 years old for furnaces (10 for heat pumps and ACs). Past that line, three questions decide it:
- How big is the repair? Major components — heat exchanger, control board, inducer motor, blower assembly — carry price tags that buy a meaningful fraction of a new system. Spending that on a 17-year-old furnace purchases the least remaining life per dollar of any option.
- What's the failure history? Repeat visits mean you're paying twice: for the repairs, and in cold nights waiting for them.
- What does winter cost you now? An aging single-stage furnace loses efficiency as components wear; a modern high-efficiency replacement recovers it and heats more evenly — and current gas furnace rebates of up to $1,600 on qualifying installations shift the math further (details in our rebates guide).
What about safety — when is the decision made for you?
One failure ends the debate: a cracked heat exchanger. The heat exchanger separates combustion gases from the air your family breathes; a crack can allow carbon monoxide into the airstream, and there is no responsible patch for it on an aging furnace. If a technician shows you a cracked exchanger (ask to see it — a trustworthy tech will show you, not just tell you), the furnace should not run until it's addressed, and on an old unit that means replacement.
Related non-negotiables: repeated flame rollout, soot streaking, or a CO alarm tied to furnace operation. Working carbon monoxide detectors on every bedroom floor are cheap insurance regardless of your furnace's age — and a proper fall maintenance visit inspects the heat exchanger and combustion safety every year precisely so problems are found on a schedule, not by an alarm.
If you do replace, what should the process look like?
Replacement done right starts with questions, not a price sheet. The new system should be sized from a load calculation — not "same size as the old one," which bakes in whatever error the original install made (see our sizing guide for why oversizing hurts). The ductwork should be evaluated at the same time, because a new furnace on leaky ducts inherits the old furnace's problems. And it's the natural moment to consider the bigger question: another gas furnace, a dual-fuel system, or a heat pump conversion — we install all three, so the recommendation follows your house, not our inventory.
As a 25-year furnace installer and Daikin & York dealer serving SW Washington and the Portland metro, we'll give you the repair quote and the replacement quote side by side when the call is genuinely close — and tell you plainly when it isn't.
About this guide
Written and reviewed by the Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255), and an authorized Daikin & York dealer. Guidance reflects the systems we install and service every week. Last reviewed July 3, 2026.
Sources & standards
Common questions
How long should a gas furnace last?
A maintained gas furnace typically serves 15–20 years. ENERGY STAR suggests starting the replacement conversation past 15 years — not because the furnace dies on schedule, but because repairs on older units buy less remaining life per dollar and efficiency has usually degraded.
Is it worth repairing a 20-year-old furnace?
For a small fix that gets you through a season while you plan — sometimes. For a major component like a heat exchanger, control board, or blower assembly — rarely. At that age a large repair spends real money on very little remaining life, and a cracked heat exchanger specifically means replacement for safety reasons.
What does a new furnace cost?
It depends on the home, equipment tier, and any duct or venting work, so we quote per project rather than publish a number that would mislead you. Gas furnace rebates of up to $1,600 are currently available on qualifying installations, and we confirm what your project qualifies for. Call (360) 944-8616 for a straight quote.
Can a cracked heat exchanger be repaired?
No — not responsibly. The heat exchanger keeps combustion gases, including carbon monoxide, out of your home's air. Once it's cracked, the furnace shouldn't run, and on an aging unit the answer is replacement. Ask the technician to show you the crack; a trustworthy one will.
