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Cracked Heat Exchanger (Why and How to Fix)


A cracked heat exchanger can be deadly.

Carbon monoxide can enter your home and potentially kill you.

Every gas furnace has a heat exchanger.

The heat exchanger is what facilitates the heat transfer to warm your home.

This guide will cover what a heat exchanger is, why a heat exchanger may crack, how to check if you have a cracked heat exchanger, and how to fix a cracked heat exchanger.

If you suspect you have a cracked heat exchanger contact a local HVAC pro.

Jump to Section

  1. What is a heat exchanger?

  2. Why a heat exchanger cracks?

  3. How to know if you have a cracked heat exchanger?

  4. How to fix a cracked heat exchanger?

  5. Conclusion

What is a heat exchanger?

A heat exchanger is a critical component in your gas furnace. It is a series of metal tubes a few inches in diameter.

The flames in your gas furnace are blown into the tubes, and the pipes heat up. The air from your home is forced through your furnace and passes over your heat exchanger.

In the process, the air gets warmed up in what’s called a heat exchanging process.

Carbon monoxide is generated inside the tubes and gets exhausted through the FLUE vent pipe to the outdoors as the gas is burned.

In the event of a cracked heat exchanger, that carbon monoxide can enter your home instead of exhausting into the outside air.

It is not the most environmentally friendly solution; however, it is how gas furnaces are designed.

If you consider upgrading, heat pumps are a much more environmentally friendly HVAC solution.

Why a heat exchanger cracks?

There are a few reasons why a heat exchanger may crack. The most common is just regular wear and tear.

Over time as you use your gas furnace, the heat exchanger will heat to very high temperatures.

As your system operates, it cycles on and off. This will cause the metal to expand and retract over and over again.

Eventually, it can crack.

Furnaces have what’s called a high-limit switch. This switch prevents the heat exchanger from reaching very hot temperatures that aren’t safe.

If your limit switch gets triggered, your furnace may crack faster as it is a sign that your heat exchanger is getting too hot.

When the high limit switch is triggered, your furnace will shut off. And it is one of the reasons why your furnace may not be working correctly.

One reason your heat exchanger may get too hot is that the gas pressures are too high. This is why it is recommended to get your HVAC system maintained yearly to ensure it is operating properly.

Another factor that may contribute to a cracked heat exchanger is humidity.

If you live in a humid area, the moisture can cause rust which will cause your heat exchanger to crack faster.

How to check if you have a cracked heat exchanger

There are a few ways to check if your heat exchanger is cracked. Usually, both methods are used together to validate if it is cracked or not.

You will most likely need the help of an HVAC professional.

The first way is with a carbon monoxide detector.

You need to turn on your Gas furnace and place the carbon monoxide detector on one of the supply registers.

If the detector is triggered, there is a good chance your heat exchanger is cracked.

The second method is a visual inspection.

Visual inspection is usually done with a camera designed to fit in tight spaces.

The camera is placed and maneuvered within the heat exchanger housing.

This allows the HVAC professional to verify if there is a crack and where it is.

The second way to visually inspect the heat exchanger is by actually removing the heat exchanger itself.

This process is much more time-consuming as it involves removing many components before you can remove the heat exchanger.

How to fix a cracked heat exchanger

There are only two ways to fix a cracked heat exchanger and get your heater up and running again.

The first one is by replacing your heat exchanger.

The second one is to get a new heating system.

There are many factors to consider when deciding to repair or replace your heating system.

Either way, you should consult with an HVAC professional.


Your heat exchanger facilitates the heat transfer process when you heat your home with a gas furnace.

A cracked heat exchanger is a serious issue that needs to be addressed as soon as possible.

Heat exchangers can crack over time because of the expansion and contraction when it heats up and cools down.

An HVAC professional will be able to diagnose a cracked heat exchanger.

You can fix a cracked heat exchanger by replacing the heat exchanger itself or getting a new gas furnace altogether.

Alternatively, you can consider a heat pump that does both heating and cooling.

If you have any questions, don’t hesitate to contact us, and we will be happy to help.

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