close up of a heat exchanger

A furnace is usually a background player at home, helping keep you warm across the cold winter months. It regularly doesn’t get noticed until a malfunction appears. 

One source could 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 you should do if you suspect that may be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps transition heat from the combustion chamber in your furnace to the air that moves inside the ventilation. It usually accomplishes this using coils or tubes that heat the air while serving as a barrier to keep byproducts created in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its key role, it’s no surprise that a damaged heat exchanger can be hazardous. Cracks in the heat exchanger can allow dangerous gasses – such as carbon monoxide, which can be lethal – to flow throughout your home. 

For obvious reasons, never use your furnace if you suspect you're dealing with a cracked heat exchanger, as letting it run could make the whole household ill. Contact an HVAC professional as soon as possible if you are worried your furnace has a cracked heat exchanger that needs to be repaired. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: A crack in your heat exchanger may cause your furnace to shut off. 
  • Odd Smells: If the air leaving your furnace has an intense chemical smell, it might be a sign gasses are seeping through cracks in your heat exchanger. These gasses, which can smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm goes off or you recognize health problems: If a cracked heat exchanger is relieving carbon monoxide into your home, your carbon monoxide alarm could go off or family members might start experiencing signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If the alarm goes off or you feel unwell, leave the home immediately and then call for help. 
  • Soot: If you see black sooty accumulating around the exterior of your furnace, it’s another sign something might 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 with extensive experience in furnace installation as soon as possible 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 generally covered by the warranty. It's a good idea to check the warranty paperwork on your furnace, since while the warranty may not cover the entire cost of repairs, it still may significantly shrink your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the easiest ways to prevent a problem in your furnace overall is via routine furnace maintenance. Furnaces offer the most benefits when they work efficiently. Calling a skilled professional to examine 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 helpful to inspect 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 drawing air through a clogged filter makes your entire furnace work harder to accomplish its job. And the harder your furnace needs to run, the more deterioration parts like the heat exchanger will sustain.