A furnace is often a background player for your home, ensuring you're warm in the cold winter months. It regularly won't be noticed until something goes wrong. 

One root cause could be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s important to familiarize yourself with the symptoms of a cracked heat exchanger and what you should do if you are worried that might be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps transition heat from the combustion chamber of your furnace to the air that moves through the air ducts. It typically accomplishes this through coils or tubes that heat up the air while acting as a barrier to keep the gasses created in the combustion chamber, called flue gasses, from leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its key role, it’s no surprise that a damaged heat exchanger can be hazardous. A damaged heat exchanger can allow dangerous gasses – like carbon monoxide, which can be lethal – to be distributed across your home. 

For obvious reasons, do NOT use your furnace if you suspect it has a cracked heat exchanger, as doing so could make the whole household sick. Contact an HVAC professional as soon as possible if you are worried your furnace has a cracked heat exchanger that needs repair. 

Four Symptoms of a Cracked Heat Exchanger: 

  • Furnace turns off: A cracked heat exchanger can cause your furnace to switch off. 
  • Strange Smells: If the air escaping your furnace has a strong chemical scent, it might be a sign gas is slipping through cracks in your heat exchanger. These gasses, which may smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm initiates or you feel symptoms of poisoning: If a cracked heat exchanger is releasing carbon monoxide into your home, your carbon monoxide alarm should go off or family members may experience signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If an alarm goes off or you feel unwell, get out of the home immediately and then call for help. 
  • Soot: If you find black sooty collecting on the exterior of your furnace, it’s another sign something may be seriously wrong.

What You Should Do if Your Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, hire a pro with extensive experience in furnace installation right away so they can inspect your system and, if needed, perform a furnace heat exchanger replacement. Costs often differ depending on the situation, but estimates run in the neighborhood of $1,000 to $3,000. 

Estimates aside, the good news is that heat exchangers are generally protected by the warranty. You’ll want to check the warranty paperwork on your furnace, since while the warranty might not cover the entire cost of repairs, it can significantly reduce your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the best ways to avoid problems in your furnace overall is with routine furnace maintenance. Furnaces provide the best possible return on investment when they work efficiently. Contacting a skilled professional to check your furnace for broken-down parts, dirty filters and other common problems can keep you from getting a big bill later on.  

It’s also beneficial to take a look at your furnace filters every few months – it’s ideal some filters be swapped out every 90 days or sooner if they are dirty or grimy. While the filters are not part of the heat exchanger itself, the strain of drawing air through a clogged filter makes your entire furnace work more vigorously to complete its job. And the harder your furnace needs to run, the more strain parts like the heat exchanger will sustain.