In today’s gas-fired furnaces, heat exchangers are one of the system’s central critical components. A gas burner flame doesn’t directly heat air moving through the furnace. Instead, the burner flame in the combustion chamber heats the heat exchanger, which in turn heats the air circulating through special passages. This not only provides optimum heating performance, it’s a vital safety feature.

Heat exchangers ensure that gases produced in the combustion chamber — including deadly carbon monoxide — are kept out of the system airflow.

What Goes Wrong?

A heat exchanger is designed for long service life. Certain manufacturers of new furnaces even offer lifetime warranty on the component. Nevertheless, a heat exchanger may fail during the service life of the furnace. Each time the furnace cycles on and the burner ignites, the metallic heat exchanger is subject to rapid heating and expansion. When the furnace cycles back off, the component cools again and contracts. Repeated expansion/contraction cycles over the years may eventually cause a crack. Also, heat exchangers may be subject to rust or corrosion.

Why It’s Dangerous

A cracked heat exchanger usually presents a clear safety hazard due to the risk of dangerous carbon monoxide gas infiltrating the furnace airflow. A careful visual inspection of the heat exchanger is part of the standard annual heating system checkup provided by a qualified HVAC contractor.

Testing the system airflow for the presence of carbon monoxide gas is yet another vital safety check to verify the condition of the heat exchanger.

What Happens Next?

In many localities, HVAC service technicians are required by law to shut down and disable any furnace with a cracked heat exchanger — a practice known as “red tagging.” It’s done to protect occupants from the hazards posed by carbon monoxide exposure. Because heat exchangers are a critical component, cost of replacement is often substantial. Therefore, in a furnace that’s exceeded more than half of its expected service life, replacing the heat exchanger alone is frequently not a financially viable option. Instead, the furnace itself should be replaced with a new unit.

For more information about issues with furnace heat exchangers, contact Powers Heating & Air.

Our goal is to help educate our customers in Peachtree City, Georgia and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Guide or call us at 770-487-2040.

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