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Dealing With A Failing Heat Exchanger? Here's What You'll Need To Know

The heat exchanger is an integral part of any gas or oil-fired furnace. Furnace heat exchangers work by transferring heat energy generated by the furnace's combustion chamber to the air blown through the heating system's ductwork. Conventional furnaces typically use a single heat exchanger while condensing furnaces utilize a primary and secondary heat exchanger for improved heat output and energy efficiency.

Like any other part of your furnace, the heat exchanger can fail for a variety of reasons. Unfortunately, heat exchanger failure is one of the most dangerous failure modes for any furnace due to an elevated risk of carbon monoxide poisoning. Read on to learn more about how heat exchangers fail and what can be done in the aftermath of a heat exchanger failure.

How Do Heat Exchangers Fail?

There are plenty of reasons why a heat exchanger fails during your furnace's life span. The following offers a few common causes to consider:

Metal fatigue - Metal expands when heated and contracts when cooled. The constant expansion and contraction place stress on the heat exchanger's metal coils, eventually resulting in stress cracks throughout the coil.

Limited airflow - A dirty furnace filter can create blockages that restrict normal airflow. Such blockages can cause the furnace itself to overheat. Heat exchangers can develop cracks when subjected to temperatures well beyond those experienced during normal operation.

Rust and corrosion - Heat exchangers can also fall victim to rust and corrosion caused by acidic condensation within the tubing.

Ordinary wear and tear - The average life span of the heat exchanger is roughly the same as the furnace itself. After 20 to 25 years of operation, the likelihood of heat exchanger failure increases dramatically.

What Are the Symptoms of Heat Exchanger Failure?

Aside from stress cracks due to metal fatigue, a failing heat exchanger can also exhibit other symptoms. Some of the symptoms are often shared with other furnace issues, so a thorough inspection is usually needed to rule out other problems.

Yellowed and flickering flames are a common symptom of cracked heat exchangers. Combustion gases can interfere with the burner's precise fuel and air mixture. The end result is a flame that changes from its normal bright blue color to a yellow color -- a clear sign of improper combustion. Flame rollout can also occur, resulting in a tripped safety switch and subsequent furnace shutdown.

A heat exchanger failure can even set off your carbon monoxide detector. If you're experiencing symptoms of carbon monoxide poisoning, even if your CO detector fails to detect a buildup of combustion gases, you should immediately shut down your furnace and seek medical attention.

Should You Replace or Repair Your Heat Exchanger?

Heat exchanger repairs are not impossible, but they're often very difficult and very expensive to perform. Since the heat exchanger resides at the heart of your furnace, the amount of time and effort required to simply access the component rarely makes repairs worthwhile. Stress cracks can also appear in places where repairs are difficult or even impossible to pull off. Even successful repairs aren't guaranteed to last, as stress cracks can form in new areas or even near the site of the original repair.

Another option involves replacing the heat exchanger entirely. Heat exchanger replacements can be somewhat economical as long as the furnace is covered under warranty. However, the average furnace warranty covers only the cost of parts, with labor usually excluded.

Heat exchanger failure is a common issue for older furnaces, which is why most HVAC professionals prefer to replace the entire furnace. A complete furnace replacement not only solves the heat exchanger problem, but it'll also render other furnace issues moot. You'll also benefit from the improved performance and energy efficiency of a new furnace.