4 Telltale Signs Your Heat Exchanger Is Cracked

The heat exchanger is a vital component of the furnace. Its primary function is to separate breathable air from combustion, a process that involves an oxidant like oxygen and fuel or reductant. The chemical process generates oxidized products that are generally gaseous. This does not always cause a fire since the flame remains invisible until the combustible substances start to vaporize. When the flame becomes visible, you know the substances are being vaporized.

Know The Ins And Outs Of Your Furnace

When the temperature in your home drops below the preferred setting, the furnace will kick on. The furnace will continue operating until the temperature reaches the desired setting. In most homes, the preferred temperature is 72 while others opt for lower settings to minimize their energy consumption. It is unfortunate when the temperature drops below the preferred setting and the furnace does not respond properly. This sign tells you an internal component has malfunctioned. While the furnace is not functioning, it does not always mean the entire unit needs to be replaced. In most cases, the malfunction is linked to a damaged component embedded inside the furnace. Knowing the signs that point to a bad heat exchanger is a great place to start. Learn more by reading the content provided in the article below.

Flame Is Not Blue, Unsteady, And Split

If there is anything you should know about your furnace it is the flame. As previously mentioned, the flame is only visible during the vaporization of combustible substances like natural gas or propane. In other words, a visible flame tells you the combustible fuel is undergoing vaporization. When the heat exchanger is operating properly, the flame will be steady and blue. An unsteady furnace flame points to a draft from an external source. Even the tiniest draft will result in an unsteady flame that will alter the functionality of the furnace. Immediately upon discovering your furnace flame is shaky, you should begin looking for a draft. An unsteady flame does not have anything to do with the heat exchanger in most cases. When the furnace flame is split, do not contribute the problem to a failing heat exchanger. Instead, the problem is simply particles of debris or dirt in the tube of the pilot light. It is recommended to only clean the pilot tube when the furnace is not in operation. A yellow furnace flame may be contributed to a failing heat exchanger. With this said, it is never a good idea to jump to conclusions. Instead of immediately pointing to a damaged heat exchanger, it is recommended to suspect the pilot tube. When the pilot tube fills up with dirt and debris, it can result in a yellow flame. If after cleaning the pilot tube the yellow flame does not instantly turn blue. Only then should you point the finger at the heat exchanger.

Foul Odor

HVAC technicians describe the order generated by a bad heat exchanger as similar to formaldehyde. If you are unfamiliar with formaldehyde odors, you should know it is like pickles. The powerful pickle-like odor can result in respiratory attacks in people with asthma and allergy attacks. Depending on the severity of the formaldehyde-like odor, you may experience nausea. To avoid a buildup of the odors, immediately open a window or door to improve ventilation until the problem has been corrected.

Dark Soot

Heat exchangers that have cracked through years of use could generate soot. The powdery substance is black in color. In some situations, soot can be in the form of tiny flakes, larger and thicker than powder granules. The soot from cracked heat exchangers is linked to improperly burning fuel like natural gas. The substance can be scattered throughout the interior of the furnace. In severe cases, the soot will leak out of the furnace on the ground. The cracked heat exchanger may also cause moisture to build up around the bottom of the furnace. A crack heat exchanger can also emit carbon monoxide, a byproduct of burning “combustion” natural gas and propane. This is where a carbon monoxide detector will come into play. Every home with a furnace heating system should have a carbon monoxide alarm. Carbon monoxide is both odorless and colorless, so it is rarely detected by the human nose.

Physical Side Effects

Some people residing in homes with a bad furnace heat exchanger have reported physical ailments. These side effects may appear before or after the damaged heat exchanger has been identified. Physical side effects of a malfunctioning heat exchanger includes the following:
  • Headache
  • Nausea
  • Dizziness
  • Confusion
  • Upper respiratory irritation (water eyes, coughing, runny nose, itchy throat, and stuffy nose)
  • Sleepiness
  • Sore throat
  • Weakness
  • Shortness of breath
These systems are associated with a bad heat exchanger, whether cracked or not. When the heat exchanger is not working, a mixture of natural gas and combustion fumes will build up inside your home. These fumes are known as “flue gasses,” which are dangerous for your health.


Not only is it important to repair or replace a malfunctioning heat exchanger for comfort but also to avoid physical ailments. It is vital that you know the signs of a potential malfunction of a heat exchanger. A heating system, including a furnace, is the heart of every home, especially in the winter season. When temperatures drop below 32 degrees Fahrenheit, your home will no longer be livable. Knowing the signs will put you one step ahead in the diagnostic process.

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