A furnace is usually a background player at home, keeping you warm during the cold winter months. It frequently isn't noticed until a malfunction appears. 

One source might be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s worthwhile to learn the evidence of a cracked heat exchanger and what you should do if you are worried that may be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger transfers heat from the combustion chamber of your furnace to the air that circulates throughout the system. It generally 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 leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its important role, it shouldn't come as a surprise that a cracked heat exchanger can pose a risk. A damaged heat exchanger can enable dangerous gasses – like carbon monoxide, which can be lethal – to flow across your home. 

For this reason, never use your furnace if you suspect there's a crack in the heat exchanger, as doing so could make the entire family sick. Reach out to an HVAC professional as soon as possible if you are worried your furnace has a cracked heat exchanger that needs to be repaired. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace switches off: A crack in your heat exchanger could cause your furnace to turn off. 
  • Odd Smells: If the air escaping your furnace has a powerful chemical smell, it could be an indicator that gasses are leaking through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm is triggered or you recognize poisoning symptoms: If a cracked heat exchanger is relieving carbon monoxide in your home, your carbon monoxide alarm could go off or family members may struggle with signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If the alarm goes off or you feel unusually tired, exit the home as soon as you can and then call for help. 
  • Soot: If you notice 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 suspect your furnace has a cracked heat exchanger, hire a professional with extensive experience in furnace installation as soon as possible so they can examine your system and, if needed, perform a furnace heat exchanger replacement. Costs should fluctuate depending on the situation, but estimates often hover around $1,000 to $3,000. 

However, the good news is that heat exchangers are generally covered by the warranty. It's a good idea to check the warranty paperwork on your furnace, as while the warranty might not 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 via routine furnace maintenance. Furnaces offer the most benefits when they work efficiently. Calling a certified professional to inspect your furnace for worn-out parts, clogs in the air filters and other likely problems can keep you from getting a big bill later on.  

It’s also beneficial to review your furnace filters every few months – it’s ideal some filters be changed 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 pulling air through a clogged filter makes the entire furnace work harder to complete its job. And the harder your furnace needs to run, the more deterioration parts like the heat exchanger will endure.