Cracked Furnace Heat Exchanger: Repair or Replace?

A cracked heat exchanger is a carbon monoxide question before it’s a cost question. Sort out the safety part first. Then you can look at the warranty, the furnace’s age and the reason it failed.

Safety first: when to leave the house

If a CO alarm goes off, or people in the house have a headache, nausea or dizziness, don’t troubleshoot. Get everyone outside to fresh air and call 911. Stay out until responders say it’s safe to go back in.

If you smell gas, leave the house and call 911 and PG&E at 1-800-743-5000 from a safe distance. Don’t flip switches or use anything that could spark until you’re well away.

No alarm and nobody sick, but a technician told you the heat exchanger is cracked? Turn the heat off at the thermostat and leave it off until it’s been checked. Goodman’s user manual says to contact a qualified servicer at once if you notice an abnormal condition, and not to remove any internal compartment covers yourself.

What the heat exchanger does, and why a crack matters

The heat exchanger is the metal path the burner’s hot exhaust travels through. Your house air passes over the outside of it, picks up the heat and never mixes with the exhaust. Carrier’s 58SU0A manual warns that “corrosive or contaminated air may cause failure of parts containing flue gas, which could leak into the living space.”

Goodman’s user manual describes carbon monoxide as a colorless, odorless gas produced when fuel doesn’t burn completely or the flame doesn’t get enough oxygen. It lists warning signs that CO may be present: headaches, nausea, dizziness and flu-like symptoms, excessive humidity or heavily frosted windows, and flue gases that won’t draw up the vent pipe.

You can’t smell CO. That’s why the CPSC advises CO alarms on every level of the home and outside sleeping areas.

What the manufacturers tell technicians to check

Both manufacturers put the furnace on a yearly inspection schedule:

• Goodman’s GM9S96 service manual says a qualified installer or service agency should inspect the furnace at least once per year, at the start of the heating season. The checklist includes the heat exchanger: “Check for corrosion and/or buildup within the heat exchanger passageways.”
• Goodman’s installation guide adds that the heat exchanger flue passageways should be inspected at the beginning of each heating season, by a qualified servicer only. It also says burner flames should be stable, quiet, soft and blue, and must not touch the sides of the heat exchanger tubes.
• Goodman’s troubleshooting chart for its GMVC96 furnaces lists a cracked heat exchanger as a possible cause of soot and/or fumes, checked by looking at the burner flames.
• Carrier’s 58SU0A manual says a qualified service person should inspect the furnace once a year.

So a tech looks at the flame, the flue and vent, and the heat exchanger itself. On a furnace call we also test CO levels. If we confirm a crack or find dangerous CO, we shut the furnace down and give you the documentation.

Why heat exchangers fail

This matters for the repair or replace decision. If the cause stays, a new heat exchanger or a new furnace faces the same conditions.

• Airflow. Goodman’s installation guide says too much duct static pressure means too little air across the heat exchanger. That causes excessive temperature rise, limit switch tripping and heat exchanger failure. Carrier warns that blower speed has to give the temperature rise on the rating plate, or the heat exchanger’s life may be shortened.
• Combustion problems. Carrier says heavy soot and carbon buildup means something is wrong that needs correcting, such as gas valve outlet pressure, poor combustion air, a damaged or wrong-size orifice, the wrong gas, or a restricted heat exchanger. Its manual says heat exchangers with heavy soot buildup should be replaced rather than cleaned.
• Contaminated air. Carrier says halogen compounds in combustion air can corrode heat exchangers and shorten furnace life. It names aerosol sprays, detergents, bleaches, cleaning solvents, salts and air fresheners as sources. If cleaning products or sprays are stored near the furnace, tell the technician.

Repair or replace: what decides it

“Repair” here means replacing the heat exchanger. It’s a real part: Goodman lists “Heat Exchanger with Recuperator Coil” among the functional replacement parts in its GM9S96 installation guide.

Start with the warranty. In both documents below, heat exchanger coverage runs longer than parts coverage, but the fine print differs:

• Goodman’s spec sheet for the GM9S96/GC9S96 lists a Lifetime Heat Exchanger Limited Warranty, “good for as long as you own your home,” plus a 10-Year Unit Replacement Limited Warranty and a 10-Year Parts Limited Warranty. It says online registration within 60 days is required for these, except in California and Québec.
• Carrier’s 59TP6C product data lists a default 20-year heat exchanger limited warranty, and a lifetime heat exchanger warranty with registration within 90 days of original installation, except where warranty benefits can’t be tied to registration. The registered coverage applies to the original purchaser or homeowner, not later owners.

Those are two models. Your furnace has its own certificate. Ask whether it covers the labor as well as the part. If the furnace is still under warranty, start with the installing dealer or the manufacturer’s warranty process before you pay anyone for a replacement.

Then look at the rest of the furnace. Replacing a heat exchanger is a big job on a furnace that may have other aging parts. On an older furnace, a new furnace usually makes more sense, because the rest of the unit is aging at the same rate. On a newer furnace with heat exchanger coverage, the part route is worth pricing.

Fix the cause either way. If high static pressure, a gas pressure problem or contaminated combustion air cracked the old one, that needs fixing in the same job.

What you can do yourself

Very little, and that’s on purpose. Goodman’s user manual limits owner maintenance to frequent filter changes. Carrier’s manual says untrained people can clean and replace air filters, and everything else goes to trained service personnel. Carrier also warns never to run the furnace without a filter.

Keep your CO alarms working, change the filter on schedule, and keep cleaning products and sprays away from the furnace area. Leave the burner compartment, the flue and the heat exchanger to a technician.

How we handle it

Our furnace repair diagnostic is $99, credited toward the repair. If replacement is on the table, the on-site replacement assessment is free, and you get a written report of findings the same day. Our reference price for a furnace replacement is $6,500. The written estimate follows the on-site assessment and shows what your project includes.

Call (925) 999-4095 and tell us what you were told about the heat exchanger. If you have the model and serial number, have them handy. Bay Area HVAC Service is the HVAC division of ADRIUM Service Solutions, CSLB #1136642.

Where this comes from

• Goodman, GM9S92/GM9S96/GC9S96 Service and Troubleshooting manual, RS6612022r2, September 2026, page 29 (annual inspection).
• Goodman, GM9S96/GC9S96 installation guide, IOG-2029D, 07/2023, pages 29, 36 and 37 (static pressure, flames, flue passages, parts list).
• Goodman, GMVC96/GCVC96 Service Instructions, RS6612010r6, November 2017, page 62 (troubleshooting chart).
• Goodman, GM9S96/GC9S96 spec sheet, SS-GM9S96/GC9S96, 2/22, page 1 (warranty).
• Goodman, Gas-Fired Warm Air Furnace User’s Information Manual, HIG-2001B, 09/2019, pages 4 and 6 (carbon monoxide, owner maintenance).
• Carrier, 58SU0A installation, start-up, operating and service instructions, Catalog No. 58SU0A-05SI, edition 11/19, pages 5, 29, 30 and 32.
• Carrier, 59TP6C Product Data, Catalog No. 59TP6C-01PD Rev A, edition 1/25, page 1 (warranty).
• U.S. Consumer Product Safety Commission, Carbon Monoxide Fact Sheet.

Key takeaways

• If a CO alarm sounds or people feel sick, get everyone outside and call 911. The furnace can wait.
• Goodman and Carrier both call for a yearly furnace inspection by a qualified servicer. Goodman's checklist includes the heat exchanger passageways.
• A heat exchanger can be replaced as a part, and many furnaces carry a long heat exchanger warranty. Registration rules and owner limits decide whether yours still applies.
• Find out why it failed. Both manuals tie heat exchanger damage to fixable conditions like poor airflow, wrong gas pressure and contaminated combustion air.
• Owner maintenance stops at the filter. Goodman's user manual says not to remove internal compartment covers.

Related questions

Need help with your system? Call (925) 999-4095 or book a visit. Repair diagnostics are $99, credited toward the repair. Installation assessments are free.

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA Section 608 Universal certification, and is factory-trained on Daikin (Houston, 2025) and Mitsubishi. He writes from direct field experience, not marketing copy.

Further reading

• Carrier Furnace Status Codes and Greenspeed Heat Pump Fault Codes , A Carrier furnace blinks a two-digit status code on an amber LED. A Greenspeed heat pump or AC sends a code like 18-11 to the Infinity thermostat. Here are both lists from Carrier's service manuals, by model, with the checks you can do before you call.
• Choosing a controller for your Mitsubishi system , Handheld remote, MHK2, wired control or the Comfort app: what to check before adding a controller to a Mitsubishi indoor unit.
• Mitsubishi heat pump lineup: which family fits your home? , Compare FX, GX, JX, HX and WX wall units, SUZ indoor styles and P-Series, then decide between a single-zone system and a multi-zone layout.