A furnace is often a background player in your home, ensuring you're warm in the cold winter months. It regularly won't be noticed until a malfunction appears. 

One cause may be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s worthwhile to familiarize yourself with the signs of a cracked heat exchanger and what you can do if you are worried that may be 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 circulates throughout the ventilation. It typically 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? 

Thanks to its key role, it isn't surprising that a broken heat exchanger can be very dangerous. Cracks in the heat exchanger can allow dangerous gasses – such as carbon monoxide, which can be lethal – to flow throughout your home. 

For that reason, never run your furnace if you suspect it has a cracked heat exchanger, as this could make the entire household ill. Reach out to an HVAC professional right away if you are worried your furnace has a cracked heat exchanger that needs repair. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace switches off: Cracks in the heat exchanger can cause your furnace to switch off. 
  • Odd Smells: If the air leaving your furnace has a powerful chemical scent, it might be evidence gasses are slipping through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm initiates or you recognize symptoms of poisoning: If a cracked heat exchanger is emitting carbon monoxide in your home, your carbon monoxide alarm could go off or household members may start experiencing signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If your alarm goes off or you feel unusually tired, leave the home right away and then call for help. 
  • Soot: If you find black sooty collecting near the exterior of your furnace, it’s more evidence something might be seriously wrong.

What You Can Do if a Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, call a professional with extensive experience in furnace installation right away so they can take a look at your system and, if necessary, perform 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 generally covered by the warranty. You should review the warranty paperwork on your furnace, since while the warranty might not cover the entire cost of repairs, it could significantly reduce your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to prevent a problem in your furnace overall is with consistent furnace maintenance. Furnaces offer the most benefits when they operate efficiently. Calling a certified professional to check your furnace for old parts, clogs in the air filters and other likely problems can keep you from getting a big bill later on.  

It’s also helpful to take a look at your furnace filters every few months – it’s recommended 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 your entire furnace work more vigorously to do its job. And the harder your furnace has to work, the more deterioration components like the heat exchanger will endure.