Should you repair or replace a cracked heat exchanger?
Updated August 2026
← Every repair-or-replace call
A cracked heat exchanger almost always means replacing the furnace, not repairing the part, and until it is handled you should not run the furnace at all. The exchanger is what keeps combustion gases, including carbon monoxide, out of the air you breathe, so a crack is a genuine safety hazard. The part is $500–1,500, but the labor to pull the furnace apart pushes the repair to $1,500–3,000, close enough to a new furnace at $4,000–8,000 that replacement is usually the smarter money past 10 years.
The short version
This is the one HVAC repair where safety, not the 50% rule, leads. A cracked heat exchanger can leak carbon monoxide into the home, so the first move is to shut the furnace off and keep it off. On the money side, the exchanger sits at the core of the furnace, and reaching it means nearly disassembling the unit, which is why a $500–1,500 part becomes a $1,500–3,000 job. If the furnace is under 8 years, the exchanger is often under a 20-year or lifetime parts warranty, which can make repair worthwhile. Past 10 years, replace the furnace: the crack signals a heat exchanger fatigued by years of expansion and contraction, and the whole unit is near the end of its 15–20 year life.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Furnace under 8 years, exchanger under parts warranty | Repair | The part is covered; you pay labor, not $1,500–3,000 in full |
| Furnace past 10 years, cracked exchanger | Replace furnace | The teardown nears a new furnace; the unit is aging anyway |
| Any age, confirmed carbon-monoxide leak | Stop using it now | A safety hazard first; shut it off before deciding on cost |
| Suspected crack, not yet confirmed | Verify first | Get a camera or combustion test before spending; be sure |
| 13–20 years, cracked exchanger | Replace furnace | End of service life; a repair is money into a finished unit |
What each path costs
Repairs typically run $1,500–3,000; a replacement is $4,000–8,000 installed. A heat exchanger is often warrantied 20 years or for the life of the original owner. Under 8 years, repair; past 10, a crack means replacing the 15–20 year furnace. 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
How dangerous is running a furnace with a cracked heat exchanger?
Dangerous enough to stop immediately. The heat exchanger separates the toxic combustion byproducts, including carbon monoxide, from the warm air the blower sends through your house. A crack can let those gases into your living space, and carbon monoxide is odorless and can be deadly. Shut the furnace off, ventilate, and make sure you have working CO detectors. Heat with electric space heaters until the furnace is repaired or replaced. Do not let anyone talk you into running it just to get through a cold snap. See the risks of ignoring it.
How do I know the heat exchanger is really cracked?
Insist on proof before you spend. A reputable technician confirms a crack with a camera inspection, a combustion analysis showing high carbon monoxide, or a chemical test, not just a hunch. Because a cracked exchanger condemns the furnace, and some unscrupulous sellers use it to force a sale, ask to see the crack on camera or the analyzer reading. Learn what a heat exchanger is and how it is inspected so you can ask the right questions. A second opinion is cheap insurance on a $4,000–8,000 decision.
Is the heat exchanger ever covered under warranty?
Often, if the furnace is fairly young. Many manufacturers warranty the heat exchanger for 20 years or even the lifetime of the original owner, sometimes requiring registration. On a furnace under 8 years, that can mean the part is free and you pay only the labor to install it, which swings the repair-or-replace math toward fixing it. Past the warranty term you carry the full $1,500–3,000, and on an older furnace that pushes toward replacement. Check your paperwork or the manufacturer's site before assuming the worst.