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What Causes Cracks in a Heat Exchanger?

A cracked heat exchanger is one of the most serious issues that your furnace can develop. In furnaces, the heat exchanger is designed to direct combustion byproducts to the exhaust flue on one side and warm air into the house on the other. A cracked heat exchanger can cause combustion byproducts like carbon monoxide to mix with the air being circulated into the house. Practically all of the combustion byproducts from a furnace are toxic, and can cause death in high amounts. In the interest of helping prevent this issue, we’ve assembled a list of causes for cracked heat exchangers.


If an air filter becomes too dirty, it can block most of the airflow through the heat exchanger. This causes heat to become trapped in the heat exchanger, where it will put the part under enormous strain. This is one of the most common causes of cracked heat exchangers. It’s also one of the reasons that changing your air filter every month is recommended.

Oversized Furnace

An oversized furnace presents a number of problems for you entire heating system. For the heat exchanger in particular, the constant short-cycling common to oversized furnaces will cause the metal pipes to rapidly expand and contract. Over time, this increased stress can open cracks. An oversized furnace can also cause the heat exchanger to overheat.


Even if you take good care of your heating system, the heat exchanger can simply crack from years of use. The natural cycle of expansion and contraction will cause the metal in your heat exchanger to wear out after enough time. It is far better to have this happen after a couple decades of use, however, than to have to potentially replace your entire furnace after 5 years due to preventable issues.

Regardless of how the problem occurs, the important thing is that you replace a cracked heat exchanger as soon as possible. It might be a pain, but the alternative is much worse. If you think you may have a cracked heat exchanger, call Comfort Flow Heating. We conduct heating repairs throughout the Eugene region.

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