A furnace is usually a background player for your home, keeping you warm during the cold winter months. It often won't be noticed until something goes wrong. 

One cause could be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s critical to learn 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 transition heat from the combustion chamber of your furnace to the air that circulates throughout the system. It usually handles this using coils or tubes that heat the air while functioning as a barrier to keep the gasses formed 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 damaged heat exchanger can be hazardous. A damaged heat exchanger can allow dangerous gasses – like carbon monoxide, which can be lethal – to flow throughout your home. 

For obvious reasons, never turn on your heater if you believe there's a crack in the heat exchanger, as this could make your entire household sick. Call an HVAC professional immediately if you believe your heating 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 shut off. 
  • Strange Smells: If the air leaving your furnace has a powerful chemical odor, it could be a sign gas is leaking through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm goes off or you notice symptoms of poisoning: If a cracked heat exchanger is relieving carbon monoxide into your home, your carbon monoxide alarm should go off or household members could start experiencing signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If your alarm goes off or you feel sick, get out of the home right away and then call for help. 
  • Soot: If you see black sooty collecting around the exterior of your furnace, it’s another sign something could 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 professional well versed in furnace installation right away so they can take a look at your system and, if required, handle a furnace heat exchanger replacement. Costs often fluctuate depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

However, the good news is that heat exchangers are often protected by the warranty. You’ll want to confirm the warranty paperwork on your furnace, since while the warranty may not 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 prevent a problem in your furnace overall is via regular furnace maintenance. Furnaces provide the best possible return on investment when they work efficiently. Hiring a certified professional to check your furnace for broken-down parts, dirty filters and other common 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 encouraged some filters be swapped out 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 the entire furnace work harder to accomplish its job. And the harder your furnace has to work, the more wear and tear components like the heat exchanger will experience.