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Why Heat Exchangers Fail

why heat exchangers fail

Furnaces are safe appliances, but under certain circumstances and the right malfunctions they can become dangerous to continue operating. The most serious malfunction would be a cracked heat exchanger. The heat exchanger is a set of metal coils in the furnace that is warmed by the combustion gases and fire from the burner. The heat exchanger is responsible for putting heated air into your home while also keeping dangerous fumes and exhaust out of your indoor air. A crack in your heat exchanger poses a serious safety threat to those in your home. It can allow carbon monoxide to leak into your home as well as other gases such as sulfur dioxide, and nitrous oxide. These combustion gases can lead to serious illness or death.  Heat exchangers are designed to provide safe furnace operation during its life expectancy, but below we discuss reasons why heat exchangers fail.

Furnace Age

An aging furnace is a common cause of heat exchanger failure due to normal wear and tear. Over the years the metal expands, and contracts so cracks and breaks will form because of the constant bending of the metal. Even great equipment that has been properly maintained over its lifespan with quality installation will fail due to its age, especially if older than 15 years old. To help prolong the furnace lifespan and avoid early furnace replacement it is important to schedule annual furnace maintenance.

Improperly Sized Furnace

An improperly sized furnace will negatively affect the furnace’s lifespan. An oversized furnace will run heating cycles too frequently also known as short cycling. This increases the chance of metal fatigue due to repeated expanding and contracting. As part of normal operation, the heat exchanger and hot flame will create a bit of condensation. An oversized furnace will not evaporate the condensation from inside the furnace completely due to short cycling. This will then create rust and too much rust over time will drill a hole in the tubing or chamber leading to a failed heat exchanger. A furnace that is too small will also damage your heat exchanger. Its smaller size will limit air from circulating properly causing your heat exchanger to overheat, crack and fail. Make sure to hire licensed, trained professionals for furnace replacement. Poor installation can affect the overall lifespan of your furnace.

Lack of Routine Maintenance

Another common reason why heat exchangers fail is simply due to dirty, clogged air filters. This is because a clogged air filter will restrict airflow causing the heat exchanger to overheat which eventually leads to cracks. Contact LA Construction, Heating and Air to schedule routine furnace maintenance.

Insufficient Airflow

Dirty air filters can also lead to insufficient combustion. If the furnace does not receive enough air this will cause the furnace internal temperature to rise. If the furnace becomes too hot, then the gas will not circulate properly causing the heat exchange to split. Another reason for insufficient airflow is a too small of a return duct causing the heat exchanger to crack sooner than it should. Insufficient airflow can lead to premature metal fatigue and early furnace replacement.


Under certain circumstances corrosion of the heat exchanger can occur. Household chemicals can bypass air filters and cause holes on the heat exchanger. Off-gassing from paint, or new carpeting can also contribute to corrosion of the heat exchanger. A frozen vertical evaporator coil can melt directly onto the heat exchanger below causing corrosion.  

Contact LA Construction, Heating and Air

Stay ahead of furnace issues and heat exchanger problems by scheduling annual furnace maintenance. In between visits be sure to check and replace your air filter before it becomes clogged with contaminants and other pollutants. If your heat exchanger fails and your furnace is older than 10 years, consider furnace replacement. Give us a call today or contact us online to schedule an appointment with one of our trained professionals. We are here to help you stay warm and cozy this winter.

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