A furnace is almost always a background player for your home, keeping you warm during the cold winter months. It regularly doesn’t get noticed until something goes wrong. 

One cause could be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s worthwhile to know the evidence of a cracked heat exchanger and what you can do if you believe that may be 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 inside the air ducts. It generally accomplishes this through coils or tubes that heat up the air while functioning as a barrier to keep the gasses produced in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its important role, it shouldn't come as a surprise that a broken heat exchanger can be hazardous. A damaged heat exchanger can permit dangerous gasses – such as carbon monoxide, which can be lethal – to circulate through your home. 

For obvious reasons, never run your furnace if you suspect you're dealing with a cracked heat exchanger, as this could make the whole household sick. Call an HVAC professional right away if you think your furnace has a cracked heat exchanger that needs repair. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace shuts off: A cracked heat exchanger could cause your furnace to switch off. 
  • Strange Smells: If the air escaping your furnace has a strong chemical odor, it may be evidence gas is seeping through cracks in your heat exchanger. These gasses, which can smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm goes off or you recognize poisoning symptoms: If a cracked heat exchanger is releasing carbon monoxide into your home, your carbon monoxide alarm should go off or household members could start experiencing signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If an alarm goes off or you feel unwell, get out of the home as soon as you can and then call for help. 
  • Soot: If you find black sooty collecting near the exterior of your furnace, it’s more evidence something could be seriously wrong.

What to Do if the Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, call a pro well versed in furnace installation as soon as possible so they can take a look at your system and, if necessary, perform a furnace heat exchanger replacement. Costs will vary depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

However, the good news is that heat exchangers are generally included in the warranty. You’ll want to confirm the warranty paperwork on your furnace, as while the warranty won't always cover the entire cost of repairs, it can significantly reduce your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the most convenient ways to minimize the risk of problems in your furnace overall is with consistent furnace maintenance. Furnaces work the best when they operate efficiently. Contacting a skilled professional to examine your furnace for worn-out parts, dirty filters and other likely problems can help you avoid getting a big bill later on.  

It’s also beneficial to review 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 are not part of the heat exchanger itself, the strain of dragging 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 endure.