A furnace is usually 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 might be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s important to know the evidence of a cracked heat exchanger and what you can do if you suspect that is 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 circulates inside the ventilation. It typically does 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 escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its key role, it isn't surprising that a cracked heat exchanger can be very dangerous. Cracks in the heat exchanger can permit dangerous gasses – such as carbon monoxide, which can be lethal – to be distributed throughout your home. 

For obvious reasons, don't ever run your heating if you believe you're dealing with a cracked heat exchanger, as this could make the entire family sick. Contact an HVAC professional right away if you believe your furnace has a cracked heat exchanger that needs repair. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace shuts off: Cracks in the heat exchanger may cause your furnace to turn off. 
  • Odd Smells: If the air leaving your furnace has a strong chemical smell, it could be a sign gas is slipping through cracks in your heat exchanger. These byproducts, which can smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm is triggered or you feel health problems: If a cracked heat exchanger is releasing carbon monoxide in your home, your carbon monoxide alarm should go off or household members might experience signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If the alarm goes off or you feel sick, get out of the home immediately and then call for help. 
  • Soot: If you notice black sooty accumulating around the exterior of your furnace, it’s an indication something may be seriously wrong.

What You Should Do if a Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, call a professional well versed in furnace installation right away so they can examine your system and, if required, perform a furnace heat exchanger replacement. Costs often differ depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

However, the good news is that heat exchangers are generally covered by the warranty. You should check the warranty paperwork on your furnace, as while the warranty won't always cover the entire cost of repairs, it can significantly lower your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to prevent a problem in your furnace overall is via routine furnace maintenance. Furnaces provide the best possible return on investment when they run efficiently. Contacting a trained professional to check your furnace for old parts, clogged filters and other likely problems can keep you from getting a big bill later on.  

It’s also a good idea to inspect your furnace filters every few months – it’s recommended some filters be swapped out every 90 days or sooner if they are dirty or grimy. While the filters aren't a 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 works, the more wear and tear pieces like the heat exchanger will sustain.