A furnace is usually a background player at home, ensuring you're warm during the cold winter months. It often isn't noticed until a malfunction appears. 

One source may be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s critical to know the symptoms of a cracked heat exchanger and what you can do if you are worried that is 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 moves throughout the air ducts. It usually accomplishes this using coils or tubes that warm the air while serving as a barrier to keep the gasses created in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its central role, it’s no surprise that a damaged heat exchanger can be very dangerous. A crack in the heat exchanger can enable dangerous gasses – like carbon monoxide, which can be lethal – to circulate throughout your home. 

For that reason, don't ever use your heating if you suspect it has a cracked heat exchanger, as this could make the whole family ill. Contact an HVAC professional right away if you are worried your heating has a cracked heat exchanger that needs repair. 

Four Symptoms of a Cracked Heat Exchanger: 

  • Furnace shuts off: A crack in your heat exchanger can cause your furnace to switch off. 
  • Strange Smells: If the air escaping your furnace has a powerful chemical scent, it may be an indicator that gas is seeping through cracks in your heat exchanger. These gasses, which will often 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 emitting carbon monoxide into your home, your carbon monoxide alarm should go off or household members might experience signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If an alarm goes off or you feel unusually tired, leave the home as soon as you can and then call for help. 
  • Soot: If you spot black sooty collecting around 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, hire a pro well versed in furnace installation right away so they can take a look at your system and, if needed, start a furnace heat exchanger replacement. Costs often differ depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are regularly covered by the warranty. It's a good idea to confirm the warranty paperwork on your furnace, since while the warranty might not cover the entire cost of repairs, it could 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 with consistent furnace maintenance. Furnaces work the best when they operate efficiently. Hiring a certified professional to examine your furnace for old 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 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 drawing air through a clogged filter makes the entire furnace work longer to accomplish its job. And the harder your furnace needs to run, the more deterioration parts like the heat exchanger will sustain.