The quick answer
Quick answer
Repair wins when the furnace is under about 10 years old and the fix is a normal wear part. Replacement wins when the unit is 15+, the repair is major, or the heat exchanger is compromised — that last one isn't a judgment call, it's a safety stop. In between, use the 50% rule: when a repair approaches half the cost of replacement on an aging unit, put the money toward the new furnace.
- Age bands: under 10 years, repair-leaning. 10–15, judgment territory — run the math. Over 15, replacement-leaning, especially for big-ticket parts.
- The 50% rule: repair quotes approaching 50% of replacement cost on an older unit rarely make sense — you're paying half price for zero new years of expected life.
- A cracked heat exchanger ends the repair conversation. That's the carbon monoxide barrier, and we treat it as a shut-it-down-today issue.
- Our published ranges: repairs $100–$2,000+, replacement $6,200–$10,600 — the overlap zone is exactly where second opinions earn their keep.
- Any repair-vs-replace quote you get from anyone — including us — deserves a line-item diagnosis. We review other companies' quotes free.
The decision factors
The part that failed
Ignitors, flame sensors, and capacitors are consumables — cheap, quick, repair without guilt at almost any age. Inducer motors, blower motors, gas valves, and control boards are the middle tier. Heat exchangers and repeated major failures are replacement territory.
Age against expected life
Wisconsin furnaces work hard and typically serve 15–20 years. A $900 repair on a 7-year-old furnace buys you a decade; the same repair on an 18-year-old furnace buys you a countdown to the next failure.
The repair history, not just this repair
Second major repair in two seasons? The unit is telling you something. Chasing failures one part at a time on an old furnace is the most expensive way to buy a new one.
Efficiency and comfort you're forgoing
If the old unit is an 80% single-stage and your bills or comfort bother you, a failure is the natural exit ramp — you were going to want the upgrade anyway. If the old unit is a 96% two-stage you love, that argues for the repair.
Timing and leverage
A January no-heat emergency is the worst seat at the negotiating table. If your furnace is 15+ and limping, a planned shoulder-season replacement beats a panic decision at 2 AM — though we do answer at 2 AM, every night of the year.
Repair the furnace vs Replace the furnace
| Situation | Repair leans right | Replacement leans right |
|---|---|---|
| Furnace age | Under ~10 years | Over ~15 years |
| This repair's cost | Minor wear part, small fraction of replacement | Approaching 50% of a new furnace |
| Repair history | First real issue | Second major repair in a couple seasons |
| Heat exchanger | Intact | Cracked or corroded — conversation over |
| Bills & comfort | You're happy with both | High bills, uneven rooms, loud cycling |
| Your horizon in the home | Selling soon (make it work, disclose honestly) | Staying — invest in the decade ahead |
The Waukesha County version of this decision
Around here the furnace isn't a comfort appliance, it's life support for your plumbing: an extended no-heat stretch in January risks frozen pipes on top of a cold family. That asymmetry is why we tell customers with 15-plus-year-old furnaces to make the repair-or-replace call before the coldest weeks, on their own schedule — and why our 24/7 line exists for everyone who couldn't. It's also why the free second opinion matters most in winter: a scary quote at your most vulnerable moment deserves a calm second set of eyes.
One more local wrinkle: replacement means a Wisconsin mechanical permit and inspection. We pull the permit as part of every install — typical municipal fee runs $90–$180 with the inspector closing it out — and a repair on existing equipment generally doesn't need one. If a replacement bid doesn't mention a permit at all, that's not a discount, that's a corner being cut with your homeowner's insurance and resale paperwork.
The honest numbers
Both published planning ranges, side by side — the decision usually lives in the overlap.
| Option | Planning range | What that covers |
|---|---|---|
| Furnace repair | $100–$2,000+ | Diagnostic plus fix — ignitors and sensors at the low end, inducer motors and gas valves at the top. |
| Furnace replacement | $6,200–$10,600 | New gas furnace installed with permit — 80% AFUE low end, 96%+ modulating top. |
Dollar ranges come straight from our published Instant Pricing tool (SE-Wisconsin planning ranges — see the homepage pricing section and Terms §3). Ballparks only, never a quote: your home's specifics set the real number, in writing, before any work begins.
Which one should you choose?
Repair the furnace
Repair it when
The unit is on the younger side, the failed part is a normal consumable, and the rest of the system checks out. A good repair on a good furnace is money well spent — we make repairs all day and stand behind them, with a 20% discount for On The Dot Club members.
Replace the furnace
Replace it when
Age, repair size, or repair frequency say the machine is done — or the heat exchanger says it for you. Replacement is also the moment every upgrade (AFUE tier, staging, a dual-fuel heat pump) becomes nearly free to consider, because you're already paying for install labor. Decide once, on purpose, with a written quote.
Also consider: the strategic repair
Sometimes a modest repair on an old furnace is the right move precisely because it buys time — one more season to plan the replacement, compare quotes properly, and schedule in shoulder season instead of a cold snap. We'll tell you plainly when a repair is a bridge and when it's throwing money at a machine that's done.
Ready when you are
Get the answer for your house.
Both options priced in writing, sized to your home, explained without a pitch — 24/7, owner-operated, licensed (WI #1482483). Already have someone else's quote? We'll review it for free.
Keep exploring
Next steps
Honest answers, before you decide
What does the diagnostic visit cost?
Our standard service fee is $169, and it's $0 for On The Dot Club members. Either way you get a written diagnosis with the failed part, the fix, and the price before any work happens — the same paperwork you'd want to hand us from another company for a free second opinion.
My furnace is 20 years old but runs fine. Replace it anyway?
Running fine is running fine — we don't replace working furnaces on age alone, and anyone who pressures you to should meet our second-opinion desk. What we do recommend at that age: an annual tune-up with a proper heat-exchanger inspection and CO check, and a replacement plan on the shelf so a failure becomes an inconvenience instead of an emergency.
Is a cracked heat exchanger really non-negotiable?
Yes. The heat exchanger is the wall between combustion gases and the air your family breathes; a crack can put carbon monoxide into your ducts. When we find one we show you — photos, camera scope, not just a verdict — and the furnace stays off until it's resolved. Replacement heat exchangers occasionally make sense under warranty on newer units; on old ones, the math never works.
Can you check another company's 'you need a new furnace' verdict?
That's exactly what our free second opinion is for. Send the quote or the diagnosis and we'll review it line by line — parts, labor, and whether the diagnosis supports the recommendation. If they're right, we'll tell you they're right. That answer costs you nothing either way.
Reviewed by Shane Herro, Owner & Lead Tech · Last updated 2026-07-14