Cracked Heat Exchanger: What It Means on Your Home Inspection Report

In a gas furnace, the hot exhaust from the burners passes through the heat exchanger, which Trane describes as a series of metal tubes deep inside the furnace, between the combustion chamber and the blower. The exhaust heats the metal from inside while house air flows over the outside and warms up. The metal walls keep the two apart, which is what keeps carbon monoxide out of the air you breathe, as Lennox explains.

Your report says the heat exchanger is cracked, or that a crack is suspected or possible. The wording matters. "Suspected" or "possible" means the inspector saw warning signs or couldn't rule a crack out; "cracked" means they believe they saw one. Either way, the next step is the same: a licensed HVAC contractor confirms it.

Why It Matters

A crack can let exhaust into the house. The heat exchanger carries exhaust and combustion byproducts, including carbon monoxide, and "a cracked heat exchanger can leak combustion gases into your home," Trane says. Goodman says your contractor should look for unusual wear or small cracks, "which could lead to a dangerous carbon monoxide leak into your home." The CPSC calls carbon monoxide "a deadly, colorless, odorless, poisonous gas."

The inspector usually can't see most of it. Under the InterNACHI Standards of Practice, one of the standards home inspectors work under, a home inspection is visual and non-invasive. Heat exchangers are on the list of things the inspector isn't required to inspect, measure, or evaluate, and the inspector isn't required to take equipment apart. Lennox notes that a cracked heat exchanger isn't always visible. So a report may describe clues instead. Trane lists these warning signs:

• short cycling (the furnace turns on and off quickly);
• banging or rattling sounds, or a strong metallic odor;
• yellow or flickering burner flames instead of a steady blue flame;
• soot around the furnace or flue pipe, or corrosion and rust;
• a carbon monoxide detector that keeps tripping;
• a visible crack.

Trane adds that these signs can also come from other furnace problems, which is why it says to have a licensed HVAC company evaluate it.

Suspected vs. confirmed. A certified technician can confirm a crack with diagnostic testing, Lennox says, "such as combustion analysis or visual inspection." Until a contractor has done that, a "suspected" crack is a reason to test, not a verdict.

What makes it more urgent: a CO alarm that sounds, or anyone in the house with headaches, dizziness, nausea, fatigue, or shortness of breath, which the CPSC lists as early CO symptoms. Get everyone outside and call 911 (see CO alarm going off). A tripped flame rollout switch is another flag: Goodman's service manual lists air leaking through the heat exchanger among the possible causes (see furnace flame rollout).

What to Do Before Closing

• Ask the inspector what they saw: a visible crack, rust, soot, flame behavior, or a CO reading, with photos.
• Have a licensed HVAC contractor evaluate the furnace and put the findings in writing. Trane suggests asking to see the crack yourself.
• Ask what the contractor recommends. Trane doesn't recommend repairing a cracked heat exchanger; it says to replace it or the whole furnace. Lennox says repairs are rarely recommended and that replacing the furnace may be necessary in some cases. Trane calls heat exchanger replacement one of the most expensive furnace repairs.
• Talk to your real estate agent about asking the seller to repair, replace, or credit it within your inspection contingency.

What to Do After You Move In

If a crack is confirmed and wasn't fixed before closing, don't run the furnace until a licensed HVAC contractor has replaced the heat exchanger or the furnace. If you suspect a crack, Lennox's first step is to shut off the furnace and open doors and windows, then call a professional. Meanwhile:

• Put CO alarms on every level and outside sleeping areas, as the CPSC recommends; our CO alarm guide covers placement.
• Never heat the house with a gas range, oven, or dryer, per the CPSC. If you use electric space heaters, give them 3 feet of clearance, plug them straight into a wall outlet, and turn them off and unplug them when you leave or go to sleep.
• Book a yearly inspection. The CPSC says to have the heating system, including chimneys and vents, inspected and serviced every year by a trained service technician.

Can You Fix It Yourself?

No. The heat exchanger sits deep inside the furnace, and the CPSC warns never to install or service combustion appliances without the proper knowledge, skills, and tools. Payne's owner's manual says only trained and qualified personnel should repair or service heating equipment; untrained owners can clean and replace air filters. That part is worth doing: Trane says a clogged filter can make a furnace overheat, a major cause of cracked heat exchangers. Our furnace filter guide shows how.

Frequently Asked Questions

Can a home inspector confirm a cracked heat exchanger?

Usually not. The InterNACHI standards don't require inspectors to evaluate heat exchangers or take the furnace apart, so most reports recommend an HVAC contractor's evaluation. Confirmation comes from that contractor's testing, such as combustion analysis or visual inspection.

Can a cracked heat exchanger be repaired?

Trane doesn't recommend trying, and Lennox says repairs are rarely recommended because the heat exchanger is a sealed component. Both point to replacing the heat exchanger or, sometimes, the whole furnace.

Is a cracked heat exchanger a deal breaker?

It's a safety issue and a major repair, so get the contractor's written findings and recommendation before your contingency ends, then decide with your agent whether to ask for a repair, a replacement, or a credit.

The Bottom Line

The heat exchanger's metal walls keep exhaust, including carbon monoxide, out of your air, and a crack can let it through. An inspector usually can't see most of it, so "suspected" means get a licensed HVAC contractor to test it before closing. If a crack is confirmed, don't run the furnace until it's fixed, and put CO alarms on every level. See more findings in our inspection report decoder.

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