A furnace is often a background player at home, ensuring you're warm across the cold winter months. It frequently isn't 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 critical to learn the signs of a cracked heat exchanger and what to do if you believe 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 circulates through the ventilation. It usually handles this using coils or tubes that heat up the air while functioning as a barrier to keep byproducts produced in the combustion chamber, called flue gasses, from leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its central role, it isn't surprising that a broken heat exchanger can pose a risk. A damaged heat exchanger can enable dangerous gasses – including carbon monoxide, which can be lethal – to be distributed across your home. 

For that reason, never run your heating if you suspect it has a cracked heat exchanger, as letting it run could make the whole household ill. Contact an HVAC professional immediately if you think your furnace has a cracked heat exchanger that should be repaired. 

Four Symptoms of a Cracked Heat Exchanger: 

  • Furnace switches off: A crack in your heat exchanger may cause your furnace to shut off. 
  • Odd Smells: If the air escaping your furnace has an intense chemical odor, it could be evidence gas is seeping through cracks in your heat exchanger. These gasses, which can smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm goes off or you notice poisoning symptoms: If a cracked heat exchanger is emitting carbon monoxide in your home, your carbon monoxide alarm may go off or household members may start experiencing signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If the alarm goes off or you feel unwell, get out of the home right away and then call for help. 
  • Soot: If you notice black sooty buildup around 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 worry your furnace has a cracked heat exchanger, hire a pro experienced in furnace installation as soon as possible so they can examine your system and, if needed, handle 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. You should confirm the warranty paperwork on your furnace, as while the warranty may 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 most convenient ways to prevent a problem in your furnace overall is with routine furnace maintenance. Furnaces work the best when they work efficiently. Contacting a trained professional to inspect your furnace for worn-out parts, clogged filters and other potential problems can help you avoid getting a big bill later on.  

It’s also a good idea to inspect your furnace filters every few months – it’s recommended some filters be replaced 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 pulling air through a clogged filter makes the entire furnace work harder to do its job. And the harder your furnace works, the more deterioration components like the heat exchanger will experience.