January 2025
By: Josh Walejewski
Read Time: 3-4 Minutes

Your furnace is arguably the most critical component of your home’s comfort, keeping you and your family warm during the coldest months. However, like any piece of equipment, it can develop issues over time—some of which can be dangerous.

A failed heat exchanger is one of the most serious problems a furnace can face. Let’s explore the essential role heat exchangers play in keeping your home warm, the common reasons they fail, the dangers they pose, and the steps to take if this happens in your home.

What Is a Heat Exchanger, and Why Is It Important?

The heat exchanger is a key part of your furnace. Its job is to transfer heat from the combustion process into the air that warms your home—while keeping harmful gases like carbon monoxide safely contained and expelled outside. Over time, the heat exchanger endures a lot of stress from heating and cooling cycles, which can eventually lead to holes and cracks.

Why Do Heat Exchangers Fail?

• Age and Wear: Over years of use, the metal can weaken and crack.
• Poor Maintenance: Lack of regular tune-ups can lead to build-up or strain that accelerates damage.
• Overheating: Restricted airflow, dirty filters, or improper system sizing can cause the furnace to overheat, stressing the heat exchanger.

Why Are Compromised Heat Exchangers Unsafe?

A failed heat exchanger has the potential for carbon monoxide (CO) or other combustion gases to leak into your home. Carbon monoxide is an odorless, colorless gas that can cause serious health problems—and even be fatal in high concentrations.

Signs of carbon monoxide exposure include:

• Headaches
• Nausea
• Dizziness
• Confusion

This is why, as HVAC professionals, we must legally and ethically “red-tag” or condemn a furnace with a compromised heat exchanger. Ignoring this issue is not an option due to the risks it poses to your family’s health and safety.

Why Aren’t Failed Heat Exchangers Typically Repaired or Replaced with a New One?

When a failed heat exchanger is discovered, customers often wonder why it can’t simply be repaired or replaced instead of replacing the entire furnace. While this might seem like a more economical solution, it’s rarely practical or cost-effective. Here’s why:

Significant Labor Costs to Remedy the Failed Heat Exchanger

The process of replacing a heat exchanger is labor-intensive and requires specialized parts. Heat exchangers are located deep inside the furnace, making them extremely difficult to access. Unlike other repairs, there’s no quick or simple way to get to the damaged part. The process involves:

• Carefully disassembling large sections of the furnace and ductwork to reach the heat exchanger.
• Removing the damaged component without compromising the surrounding parts.
• Installing the new heat exchanger and ensuring it’s properly sealed and aligned.
• Reassembling the furnace and ductwork and testing it to ensure it’s functioning safely and efficiently.

This meticulous process can take many hours of skilled labor, contributing significantly to the overall cost.

On average, this repair can cost around $2,500. For comparison, the average cost of a brand-new furnace is about $5,000 – $6,000.

Heat Exchangers Usually Fail on Older/Aging Equipment

Given that a heat exchanger is one of the most critical and expensive components of a furnace, the cost of repair often doesn’t justify extending the life of an aging system with other components that may soon fail. If your furnace is already nearing the end of its lifespan (typically 15-20 years), repairing or replacing the heat exchanger doesn’t address the wear and tear on the rest of the system.

It’s worth noting, when a heat exchanger fails, it often puts additional strain on other components of the furnace. Parts like the blower motor, control board, or igniter may already be operating under stress in an aging system, making them more prone to failure after the heat exchanger has been replaced. This domino effect can lead to frequent and costly repairs, further reinforcing why a full furnace replacement is often the more reliable and cost-effective choice.

In another blog, we provide two good rules of thumb for homeowners to use when determining whether to repair or replace their furnace or AC.

Warranty Limitations

Most furnace manufacturers offer a limited lifetime warranty on heat exchangers, but this typically applies only to the original owner of the furnace. If you’ve purchased a home where the furnace was already installed, you may not qualify for the lifetime coverage. Instead, the warranty often reverts to a shorter period, such as 20 years. For furnaces older than this, repair or replacement of the heat exchanger is usually not covered.

The Long-Term Value of Replacement

Upgrading to a new furnace isn’t just about fixing the immediate problem; it’s an investment in your home’s comfort and energy efficiency. New systems offer:

• Higher Energy Efficiency: Modern furnaces use less energy to heat your home, which can save you money on utility bills over time.
• Improved Performance: Quieter operation, better airflow, and consistent temperatures throughout your home.
• Peace of Mind: You’ll have a new warranty and confidence that your heating system will operate safely and reliably for many more years.

What to Do If a Technician Discovers a Failed Heat Exchanger

If a technician determines your heat exchanger is cracked or has failed, it’s important to handle the situation with care and confidence. Here’s how to proceed:

Take the Situation Seriously

A cracked heat exchanger is a significant safety hazard—not a sales opportunity. At Kettle Moraine Heating & Air Conditioning, we prioritize your safety above all else. Unfortunately, less reputable companies may use this as a high-pressure sales tactic, but our goal is to inform and protect you.

Request Clear Documentation

Reputable service providers should have a thorough process in place when diagnosing a failed heat exchanger. Ask for a detailed report, and whenever possible, request pictures or videos of the issue. Many technicians can provide time-stamped images with location details to confirm that the photos are from your home. If you have any doubts, ask to view the “image details” to ensure the documentation is legitimate.

Understand Your Options

We’ll guide you through all the available solutions, whether it’s a repair or full furnace replacement. This includes discussing costs, available rebates, financing options, and warranty coverage to help you make an informed decision that works for your home and budget.

Seek a Second Opinion

While we take pride in our integrity and professionalism, we understand that a major repair or replacement can feel overwhelming. If you’re unsure, don’t hesitate to get a second or even third opinion from another trusted HVAC provider. However, do not ignore the issue entirely—your family’s safety is too important to take chances.

How to Protect Yourself from Unethical Practices

Unfortunately, not all companies operate with integrity. Some less reputable providers may exaggerate or fabricate issues to push unnecessary sales. According to the leading authority on HVAC, the AHRI ‘s 2023 Guideline for Furnace Heat Exchanger Inspection states “Any crack or hole that is big enough to affect combustion is visible to the naked eye. Do not use water, cameras, or smoking agents to check for leaks. Furnace heat exchangers joints are not hermetically sealed, so a small amount of leakage can occur. Replace the heat exchanger or the furnace if there are any splits, cracks or holes.” Here’s how to ensure you’re not being taken advantage of:

• Verify the Evidence: Insist on clear, verifiable proof of the issue, such as photos or videos of your furnace’s heat exchanger.
• Ask for the Combustion Analysis Results: A significant enough crack or hole will disrupt the flame and produce a carbon monoxide reading in the flue above 100-200ppm. The technician should be able to show you the flame roll-out and the carbon monoxide reading on his combustion analyzer.
• Ask Questions: A trustworthy technician will take the time to explain the problem in plain language, without rushing you into a decision.
• Beware of High-Pressure Tactics: If you feel like the technician is more focused on making a sale than addressing your concerns, it’s a red flag.

At Kettle Moraine Heating & Air Conditioning, we believe in transparency, education, and ethical practices. We’re here to answer your questions, provide evidence, and ensure you feel confident in the decisions you make about your home’s comfort and safety.

Preventing Heat Exchanger Issues

The best way to avoid a cracked heat exchanger is through regular maintenance and attention to your heating system. Here are a few steps you can take to keep your furnace—and your family—safe:

Schedule Annual Tune-Ups

Routine maintenance allows our technicians to catch small issues, like restricted airflow or dirt buildup, before they lead to larger problems. This also ensures your furnace operates efficiently throughout the season. Has it been a while since you’ve had maintenance performed? Click here to save instantly by enrolling in a Peace of Mind Membership.

Replace Your Air Filters Regularly

A clogged filter can restrict airflow, causing your furnace to overheat and putting unnecessary stress on the heat exchanger as well as other components. If you’re due for a new filter, click here to get them delivered straight to your doorstep.

Install Carbon Monoxide (CO) Detectors

Even with proper furnace care, a carbon monoxide detector is a critical safety measure for every home. Here’s why:

• Early Warning of CO Leaks: CO is an odorless, colorless gas that can be deadly. Detectors provide the first line of defense in case of a leak from your furnace or other appliances.
• Placement Matters: CO detectors should be installed outside each sleeping area, on every level of your home, and near any attached garage. Avoid placing them too close to fuel-burning appliances to prevent false alarms.
• Check Batteries Regularly: Test your detectors monthly and replace the batteries at least twice a year. A good rule of thumb is to do this when you change your clocks for daylight saving time. If you want to take the hassle out of changing batteries, our electrical team is happy to install hardwired CO detectors with battery backup.

Conclusion

A failed heat exchanger is a serious issue, but with the right information and guidance, you can make an informed decision to protect your home and family. If you’re ever faced with this situation or have concerns about your furnace, give us a call. We’re here to help you navigate this challenge with transparency and care.

Read more blog posts from Kettle Moraine Heating & AC.

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About the Author
Josh Walejewski

Josh is a professional marketer who has worked in the HVAC industry since 2017. With a Bachelor of Applied Arts and Sciences Degree (B.A.A.S) in marketing and sustainable business management from the University of Wisconsin, he has a passion for all aspects of HVAC, business, marketing, and environmental stewardship.