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What Are the Signs of a Cracked Heat Exchanger?

A cracked heat exchanger is a dangerous problem that can occur in a gas furnace. Even the most minute crack can pose a deadly risk of carbon monoxide exposure. Due to the severity of this risk, it is important you know the signs of a cracked heat exchanger, when to call for repairs and how to prevent this issue as best as possible.

What Does a Heat Exchanger Do?

The furnace’s heat exchanger transfers heat from combustion to the air. Combustion gases enter the heat exchanger, warming its metal, and air collects heat as it comes into contact with the warm heat exchanger. The heat exchanger is fully sealed and connected to the furnace’s flue to allow the safe ventilation of combustion gases.

When stress cracks form in the heat exchanger, it is possible for combustion gases to escape and mix with the home’s air supply. Byproducts of combustion include carbon monoxide exposure, which can be deadly. 

Warning Signs of Cracked Heat Exchangers

A cracked heat exchanger is often the result of stress to the component. This dangerous issue may display warning signs you can detect, including:

Visible Damage

You may be able to see cracks in the heat exchanger when you visually inspect the furnace. Cracks occur as the metal wears due to constant expansion and contraction. Corrosion may also be present, caused by moisture from the combustion byproducts or chloride-containing fumes.


The presence of soot on the heat exchanger or on the furnace’s interiors is a warning sign of incomplete combustion. It can also be caused by improper burner adjustment or a cracked heat exchanger.

Abnormal Flame

The ignition flame should normally be a steady blue flame, which indicates proper performance. A yellow flame could mean that the burner is dirty or there is a damaged heat exchanger. A flickering flame is also a sign of malfunction.

Noticeable Odors

Cracked heat exchangers can give off a strong, chemical smell. Some say the odor is similar to formaldehyde. The odor itself can cause headaches and other physical symptoms.

Flu-like Symptoms

Headaches, nausea, dizziness, shortness of breath, fatigue, and other symptoms like what you feel with the flu can be signs of carbon monoxide poisoning. Carbon monoxide poisoning is possible when the heat exchanger is cracked or damaged.

Water on the Floor

If water has accumulated on the floor at the base of your furnace and is not linked to a condensate drain issue, a cracked heat exchanger is the likely cause.

What to Do If You Notice These Signs

With a cracked heat exchanger, operating your heating system could be dangerous. If you notice any of the above signs, you should turn off your furnace right away and call for an inspection. Do not use the heating system until it has been cleared or repaired by a professional.

Preventing Heat Exchanger Issues

The best safeguard against cracked heat exchangers is regular furnace maintenance. Your annual maintenance tune ups give your HVAC technician the opportunity to inspect the heat exchanger and other important components so damage can be identified and the component replaced before it creates a hazard. Ensure your furnace receives the care it needs each year when you sign up for a Preventative Maintenance Agreement.

Stay Safe with Star

Star Heating & Cooling keeps Indianapolis families safe with quality heating maintenance, repair, and inspection services. If you suspect your furnace has heat exchanger cracks, don’t wait – contact us right away to schedule HVAC service. For all of your home’s heating and cooling needs, call us today.