A furnace is usually a background player in your home, ensuring you're warm in the cold winter months. It frequently isn't noticed until something goes wrong. 

One root cause might be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s important to know the evidence of a cracked heat exchanger and what you should do if you believe 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 moves through the air ducts. It usually handles this through coils or tubes that heat the air while acting as a barrier to keep gas formed in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its important role, it isn't surprising that a damaged heat exchanger can pose a risk. Cracks in the heat exchanger can enable dangerous gasses – including carbon monoxide, which can be lethal – to circulate across 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 the entire family sick. Call an HVAC professional immediately if you think your furnace has a cracked heat exchanger that needs to be repaired. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace shuts off: A cracked heat exchanger could cause your furnace to turn off. 
  • Strange Smells: If the air coming out of your furnace has a powerful chemical scent, it might be evidence gas is slipping through cracks in your heat exchanger. These gasses, which may smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm is triggered or you recognize health problems: If a cracked heat exchanger is releasing carbon monoxide into your home, your carbon monoxide alarm could go off or household members might experience signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If an alarm goes off or you feel unwell, exit the home as soon as you can and then call for help. 
  • Soot: If you find black sooty collecting around the exterior of your furnace, it’s an indication something might be seriously wrong.

What You Can Do if Your Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, call a professional with extensive experience in furnace installation right away so they can examine your system and, if required, start a furnace heat exchanger replacement. Costs should differ depending on the situation, but estimates run in the neighborhood of $1,000 to $3,000. 

However, the good news is that heat exchangers are often covered by the warranty. You should review the warranty paperwork on your furnace, as while the warranty might not cover the entire cost of repairs, it still may significantly shrink your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the easiest ways to avoid problems in your furnace overall is through consistent furnace maintenance. Furnaces offer the most benefits when they run efficiently. Contacting a trained professional to check your furnace for broken-down parts, clogs in the air filters and other common 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 encouraged some filters be changed every 90 days or sooner if they are dirty or grimy. While the filters aren't a part of the heat exchanger itself, the strain of dragging air through a clogged filter makes the entire furnace work longer to do its job. And the harder your furnace works, the more strain components like the heat exchanger will experience.