The short answer
Repair a furnace when the fault is a single, common part and the furnace is safe and not near the end of its life. Replace it when the heat exchanger is cracked, when repairs keep coming, or when a large repair lands on an old unit.
ENERGY STAR suggests considering replacement once a furnace passes about 15 years. Safety comes before arithmetic: a furnace that may leak carbon monoxide is not a repair-or-replace question.
Which furnace repairs are usually worth doing?
Many no-heat calls come down to small parts with clear tests: a dirty flame sensor, a failed hot-surface ignitor, a stuck pressure switch, a tripped limit switch from a clogged filter, a failed capacitor on the blower motor, or a control board fault.
On a furnace in good condition, these are routine repairs and replacement rarely makes sense.
Larger repairs, such as the inducer motor, blower motor or gas valve, sit in the middle. On a younger furnace they are worth doing. On an older furnace they are where the decision becomes real.
When is replacement the safer answer?
A cracked or corroded heat exchanger is the main case. The heat exchanger keeps combustion gases, including carbon monoxide, out of the air you breathe. If a technician finds and documents a crack, most will shut the furnace off.
Ask to see the evidence (a camera image, a combustion analyzer reading or both) and get a second opinion if you are unsure, but do not run a furnace suspected of leaking CO.
CPSC advises CO alarms on every level of the home and outside sleeping areas. If an alarm sounds, leave the house and call 911 or the fire department from outside.
Repair or replace: the signals
| Signal | Leans repair | Leans replace |
|---|---|---|
| Age | Well under 15 years | Around or past 15 years |
| Fault | One small part with a clear test | Heat exchanger, or several major parts |
| History | First repair in years | Repeated calls each winter |
| Comfort | House heats evenly | Cold rooms, noise, short cycling |
| Efficiency | Already a condensing unit | An older, lower-AFUE unit |
| Cooling | AC is young | AC is also old: replace both together, or consider a heat pump |
How do you put numbers on it?
One common rule of thumb multiplies the repair price by the furnace’s age and compares the result with the price of a new furnace. It is a quick filter, not an answer.
Better: estimate how many more winters the repaired furnace is likely to give, divide the repair price by that, and compare it with what a new furnace would cost per year of its own life, plus any fuel saving. The repair or replace calculator walks through it with your quote.
What drives a replacement price is size, efficiency tier, venting changes (a condensing furnace needs PVC venting and a condensate drain), the AC coil on top and labor.
We publish no prices here: we do not yet hold enough sourced, dated quotes to state one honestly. Use the cost hub and the HVAC cost calculator with your own quotes.
What you can check before calling
Set to heat, set above room temperature, with fresh batteries if it uses them.
A clogged filter trips the limit switch. Replace it.
Make sure the service switch near the furnace is on. You may reset a tripped breaker once; if it trips again, leave it off.
Do not troubleshoot. Leave the house and call the gas utility or 911 from outside.
Where each option wins
Repair wins when
The furnace is safe, the fault is one part, and the unit is far from the end of its life.
You plan to move soon.
You are planning a bigger change, such as a heat pump, and need a few more winters.
Replacement wins when
The heat exchanger is cracked or the furnace is unsafe.
Big repairs keep coming on an older unit.
The AC is due too, and replacing both at once saves a second visit and gets a matched system.
Questions
How long should a furnace last?
Is a cracked heat exchanger dangerous?
Is it worth repairing a 20-year-old furnace?
Should I replace my AC at the same time?
What is the 5,000 rule?
Written and audited by
HYRE HVAC Research Desk
Primary-source research, data analysis and fact checking
We are a research desk, not a sales floor. We read the federal microdata file, the statute or the manufacturer data sheet ourselves, and we publish the figure with the document it came from and the date we retrieved it.
Where a number cannot be traced to a primary source, we publish the shorter page and say what we could not verify.
The counts below are generated from the published pages themselves, last counted October 26, 2026, and they are what we have actually published rather than what we intend to.
- 18
- studies published
- 15
- federal sources read and cited
- 15
- studies published with their full dataset as CSV
- 51
- jurisdictions reproduced against EIA’s own tables
How this desk works
- Primary sources only. Federal data comes from the agency that collects it, in the file that agency publishes. We do not cite an article that cites a source; we download the source and compute the figure ourselves.
- We validate against the agency before we publish. First, we use each federal microdata file to reproduce the agency’s own published tables. Our cooling research reproduces EIA’s state estimates and standard errors for all 51 jurisdictions. That check caught a variance formula that was off by a factor of four.
- Every estimate carries its uncertainty. These are survey figures, not counts. Standard errors are computed from the replicate weights the federal file supplies and printed beside the estimate. An estimate too imprecise to publish is reported as such rather than printed.
- Nothing is typed by hand. Prose, tables and charts all read from one dataset built by script, so a number in a sentence and the same number in the table below it cannot disagree.
- We publish the data, not just the conclusion. 15 of our 18 studies offer the full computed table as a CSV download on the page, so you can check the analysis or disagree with it. A study without a row-level dataset gets no download link and claims none in its structured data.
- We correct in public. Where we have published a figure wrongly we fix the figure, rewrite any analysis that rested on it rather than patching the number underneath it, and leave a dated correction note on the page.
- We do not install or sell HVAC equipment, and we take no payment for placement, ranking or a favorable mention. Nobody buys a position on this site.
Data as of Sources checked October 26, 2026. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold. Our editorial policy sets out how we source, date and correct what we publish.
Sources & retrieval dates
Want a contractor to look at it?
Tell us the job, the equipment and your zip code. Contractor matching is still being built, so this is an inquiry, not a booking, and nobody is dispatched from it.
HyreHVAC is a publisher. We do not install, repair or inspect HVAC equipment and hold no contractor licence. Nothing here replaces an on-site diagnosis by a licensed contractor. Sources are cited with the date they were checked.