A furnace is often a background player at home, ensuring you're warm during the cold winter months. It regularly doesn’t get noticed until something breaks down. 

One root cause may be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s worthwhile to know the evidence of a cracked heat exchanger and what you can do if you suspect that is the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps move heat from the combustion chamber of your furnace to the air that moves through the air ducts. It usually handles this through coils or tubes that warm the air while serving as a barrier to keep gas created in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Given its important role, it’s no surprise that a cracked heat exchanger can pose a risk. Cracks in the heat exchanger can allow dangerous gasses – like carbon monoxide, which can be lethal – to flow across your home. 

For that reason, do NOT use your heating if you believe there's a crack in the heat exchanger, as doing so could make the whole household ill. Call an HVAC professional right away if you are worried your heating has a cracked heat exchanger that needs repair. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: Cracks in the heat exchanger may cause your furnace to turn off. 
  • Strange Smells: If the air escaping your furnace has a powerful chemical smell, it could be a sign gasses are slipping through cracks in your heat exchanger. These byproducts, which will often smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm initiates or you notice health problems: If a cracked heat exchanger is emitting carbon monoxide in your home, your carbon monoxide alarm may go off or family members could start experiencing signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If an alarm goes off or you feel unwell, leave the home immediately and then call for help. 
  • Soot: If you see black sooty accumulating near the exterior of your furnace, it’s another sign something could be seriously wrong.

What You Should Do if a Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, hire a pro with extensive experience in furnace installation right away so they can take a look at your system and, if needed, handle a furnace heat exchanger replacement. Costs often vary depending on the situation, but estimates often hover around $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are generally included in the warranty. You’ll want to check the warranty paperwork on your furnace, since while the warranty may not cover the entire cost of repairs, it could significantly reduce your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the easiest ways to prevent a problem in your furnace overall is via routine furnace maintenance. Furnaces work the best when they work efficiently. Hiring a skilled professional to examine your furnace for worn-out parts, clogs in the air filters and other likely problems can help you avoid 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 dragging 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 components like the heat exchanger will sustain.