A furnace is almost always a background player at home, ensuring you're warm during the cold winter months. It often doesn’t get noticed until something breaks down. 

One cause might be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s important to know the symptoms of a cracked heat exchanger and what to do if you are worried that is the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps move heat from the combustion chamber in your furnace to the air that moves through the system. It typically handles this with coils or tubes that warm the air while acting as a barrier to keep byproducts produced in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its key role, it’s no surprise that a broken heat exchanger can pose a risk. A crack in the heat exchanger can allow dangerous gasses – including carbon monoxide, which can be lethal – to flow through your home. 

For that reason, never turn on your furnace if you think you're dealing with a cracked heat exchanger, as this could make the entire household ill. Contact an HVAC professional as soon as possible if you believe your heating has a cracked heat exchanger that needs repair. 

Four Symptoms of a Cracked Heat Exchanger: 

  • Furnace turns off: A cracked heat exchanger may cause your furnace to shut off. 
  • Strange Smells: If the air leaving your furnace has an intense chemical smell, it may be an indicator that gasses are leaking through cracks in your heat exchanger. These byproducts, which can smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm is triggered or you notice health problems: If a cracked heat exchanger is releasing carbon monoxide inside your home, your carbon monoxide alarm could go off or family members could experience signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If your alarm goes off or you feel sick, exit the home immediately and then call for help. 
  • Soot: If you see black sooty buildup near the exterior of your furnace, it’s an indication something may 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 pro experienced in furnace installation as soon as possible so they can inspect your system and, if required, handle a furnace heat exchanger replacement. Costs should fluctuate depending on the situation, but estimates often hover around $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are often included in the warranty. You’ll want to check the warranty paperwork on your furnace, as while the warranty won't always 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 avoid problems in your furnace overall is with regular furnace maintenance. Furnaces offer the most benefits when they work efficiently. Contacting a skilled professional to inspect your furnace for worn-out parts, dirty filters and other common problems can keep you from getting a big bill later on.  

It’s also a good idea to review your furnace filters every few months – it’s ideal some filters be swapped out 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 drawing air through a clogged filter makes the entire furnace work more vigorously to accomplish its job. And the harder your furnace needs to run, the more deterioration pieces like the heat exchanger will experience.