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How do I know if my heat exchanger is bad?

Another company has condemned my heat exchanger, what should I do? Is my heat exchanger actually bad?

These are great questions. Heat exchangers for residential forced air furnaces are metal and provide a sealed barrier between the flame and combustion gases generated by the burners in your furnace, and the air in your house that is heated. Over time, the heat exchanger metal can corrode and crack. When this happens, dangerous combustion gases, such as carbon monoxide can escape into the air in your home. Heat exchangers are often very difficult to inspect visually without the use of a special camera or disassembling the furnace. If you have questions about the integrity of the heat exchanger in your furnace there are some simple tests that can be performed. The standing flame test is simple to perform and is accurate.

Steps for conducting the standing flame test:

  • Set the thermostat to only run the furnace fan/blower.
  • Set the thermostat to only run the furnace fan/blower.
  • Shut of the gas to the furnace.
  • With only the furnace fan blowing, hold a lighter in front of each of the heat exchanger burner inlets.
  • If the lighter consistently flickers in front of one, or all, of the burners, this is indicative of a cracked/failed heat exchanger, as this demonstrates that blower air is penetrating what should be the sealed surface of the heat exchanger.

If you have questions about a heat exchanger issue/diagnosis, and don’t feel comfortable performing this test, consult a qualified HVAC technician and ask them to perform it for you.

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