A furnace is usually a background player in your home, keeping you warm during the cold winter months. It regularly doesn’t get noticed until a malfunction appears. 

One cause might be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s important to learn the evidence of a cracked heat exchanger and what you should 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 inside the ventilation. It typically does this through coils or tubes that warm the air while acting 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 central role, it’s no surprise that a broken heat exchanger can be hazardous. A damaged heat exchanger can permit dangerous gasses – including carbon monoxide, which can be lethal – to circulate throughout your home. 

For obvious reasons, never use your furnace if you believe it has a cracked heat exchanger, as doing so could make your entire household sick. Contact an HVAC professional immediately if you are worried your heater has a cracked heat exchanger that needs to be repaired. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace shuts off: A crack in your heat exchanger can cause your furnace to shut off. 
  • Odd Smells: If the air coming out of your furnace has a strong chemical scent, it could be an indicator that gas is slipping through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm goes off or you notice symptoms of poisoning: If a cracked heat exchanger is releasing carbon monoxide into your home, your carbon monoxide alarm could go off or household members could experience signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If an alarm goes off or you feel unusually tired, get out of the home immediately and then call for help. 
  • Soot: If you spot black sooty collecting around the exterior of your furnace, it’s an indication something could be seriously wrong.

What You Should Do if Your Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, call a professional experienced in furnace installation right away so they can examine your system and, if required, handle 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 generally included in the warranty. You’ll want to check the warranty paperwork on your furnace, as while the warranty may not cover the entire cost of repairs, it can significantly shrink your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the most convenient ways to minimize the risk of problems in your furnace overall is through routine furnace maintenance. Furnaces offer the most benefits when they run efficiently. Hiring a trained professional to inspect your furnace for worn-out parts, clogs in the air filters and other potential 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 changed 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 longer to do its job. And the harder your furnace needs to run, the more strain components like the heat exchanger will endure.