A furnace is almost always a background player in your home, ensuring you're warm during the cold winter months. It frequently doesn’t get noticed until something goes wrong. 

One root cause could be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s worthwhile to familiarize yourself with the evidence of a cracked heat exchanger and what you can do if you suspect that might be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger transfers heat from the combustion chamber inside your furnace to the air that moves inside the ventilation. It generally handles this via coils or tubes that heat the air while serving as a barrier to keep byproducts produced in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its central role, it’s no surprise that a cracked heat exchanger can pose a risk. A damaged heat exchanger can enable dangerous gasses – such as carbon monoxide, which can be lethal – to circulate through your home. 

For this reason, don't ever use your heating if you believe you're dealing with a cracked heat exchanger, as letting it run could make the whole household sick. Reach out to an HVAC professional right away if you are worried your heater has a cracked heat exchanger that needs to be repaired. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace switches off: A cracked heat exchanger could cause your furnace to switch off. 
  • Odd Smells: If the air escaping your furnace has a strong chemical odor, it could be a sign gasses are leaking through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm goes off or you recognize health problems: If a cracked heat exchanger is emitting carbon monoxide into your home, your carbon monoxide alarm could go off or family members could struggle with 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 right away and then call for help. 
  • Soot: If you see black sooty buildup 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 worry your furnace has a cracked heat exchanger, call a pro with extensive experience in furnace installation right away so they can take a look at your system and, if necessary, handle a furnace heat exchanger replacement. Costs often fluctuate depending on the situation, but estimates often hover around $1,000 to $3,000. 

However, the good news is that heat exchangers are regularly included in the warranty. You should confirm the warranty paperwork on your furnace, as while the warranty might not cover the entire cost of repairs, it can significantly reduce your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to avoid problems in your furnace overall is via routine furnace maintenance. Furnaces offer the most benefits when they run efficiently. Calling a skilled professional to inspect your furnace for broken-down parts, clogged filters and other likely problems can keep you from 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 replaced 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 the entire furnace work longer to do its job. And the harder your furnace has to work, the more wear and tear pieces like the heat exchanger will endure.