A furnace is usually a background player for your home, keeping you warm across the cold winter months. It often isn't noticed until something breaks down. 

One source may be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s critical to familiarize yourself with the symptoms of a cracked heat exchanger and what you should do if you suspect that is 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 flows through the ventilation. It usually does this via coils or tubes that heat the air while functioning as a barrier to keep byproducts formed in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its central role, it shouldn't come as a surprise that a broken heat exchanger can pose a risk. Cracks in the heat exchanger can enable dangerous gasses – including carbon monoxide, which can be lethal – to be distributed through your home. 

For that reason, don't ever use your furnace if you suspect there's a crack in the heat exchanger, as this could make your entire household ill. Reach out to an HVAC professional as soon as possible if you believe your furnace has a cracked heat exchanger that needs to be repaired. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: A cracked heat exchanger could cause your furnace to switch off. 
  • Strange Smells: If the air coming out of your furnace has an intense chemical odor, it might be an indicator that gas is slipping through cracks in your heat exchanger. These gasses, which will often smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm goes off or you feel symptoms of poisoning: If a cracked heat exchanger is relieving carbon monoxide into your home, your carbon monoxide alarm should go off or household members may struggle with signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If an alarm goes off or you feel unwell, exit the home immediately and then call for help. 
  • Soot: If you see black sooty accumulating around the exterior of your furnace, it’s another sign something may be seriously wrong.

What You Can Do if Your Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, hire a professional well versed in furnace installation right away so they can take a look at your system and, if required, perform a furnace heat exchanger replacement. Costs will fluctuate depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are regularly covered by the warranty. You’ll want to confirm the warranty paperwork on your furnace, because while the warranty may 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 easiest ways to minimize the risk of problems in your furnace overall is through routine furnace maintenance. Furnaces work the best when they operate efficiently. Hiring a trained professional to check your furnace for broken-down parts, dirty filters and other potential problems can help you avoid getting a big bill later on.  

It’s also beneficial to review your furnace filters every few months – it’s encouraged some filters be replaced 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 dragging air through a clogged filter makes the entire furnace work harder to accomplish its job. And the harder your furnace works, the more strain components like the heat exchanger will endure.