A furnace is often a background player in your home, helping keep you warm across the cold winter months. It often doesn’t get noticed until something goes wrong. 

One cause may be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s worthwhile to familiarize yourself with the symptoms of a cracked heat exchanger and what you can do if you are worried that might be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps move heat from the combustion chamber inside your furnace to the air that flows through the air ducts. It usually does this through coils or tubes that warm 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? 

Because of its key role, it’s no surprise that a cracked heat exchanger can pose a risk. A damaged heat exchanger can enable dangerous gasses – such as carbon monoxide, which can be lethal – to flow through your home. 

For that reason, never turn on your furnace if you suspect there's a crack in the heat exchanger, as letting it run could make your entire family sick. Reach out to an HVAC professional right away if you are worried your furnace has a cracked heat exchanger that needs repair. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: A cracked heat exchanger may cause your furnace to turn off. 
  • Strange Smells: If the air coming out of your furnace has a strong chemical smell, it might be evidence gasses are slipping through cracks in your heat exchanger. These byproducts, which can smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm is triggered or you notice symptoms of poisoning: If a cracked heat exchanger is emitting carbon monoxide into your home, your carbon monoxide alarm should go off or family members may experience signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If an alarm goes off or you feel unusually tired, exit the home as soon as you can and then call for help. 
  • Soot: If you find black sooty accumulating near the exterior of your furnace, it’s another sign something could be seriously wrong.

What You Should Do if the Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, contact a professional with extensive experience in furnace installation right away so they can examine your system and, if needed, start a furnace heat exchanger replacement. Costs often fluctuate depending on the situation, but estimates often hover around $1,000 to $3,000. 

However, the good news is that heat exchangers are often protected by the warranty. You’ll want to review the warranty paperwork on your furnace, as while the warranty won't always cover the entire cost of repairs, it can significantly reduce your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the easiest ways to avoid problems in your furnace overall is through routine furnace maintenance. Furnaces offer the most benefits when they run efficiently. Calling a skilled professional to examine your furnace for old parts, clogged filters and other potential 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 aren't connected to the heat exchanger itself, the strain of drawing air through a clogged filter makes the entire furnace work longer to complete its job. And the harder your furnace works, the more strain components like the heat exchanger will experience.