A furnace is often a background player in your home, keeping you warm across the cold winter months. It regularly 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 important to know the evidence of a cracked heat exchanger and what you can do if you are worried that is the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger transfers heat from the combustion chamber in your furnace to the air that circulates inside the ventilation. It typically handles this through coils or tubes that warm the air while serving as a barrier to keep the gasses formed in the combustion chamber, called flue gasses, from leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Given its important role, it isn't surprising that a broken heat exchanger can pose a risk. A damaged 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 turn on your heating if you suspect there's a crack in the heat exchanger, as this could make the whole household ill. Contact an HVAC professional immediately if you believe your heater has a cracked heat exchanger that needs to be repaired. 

Four Signs of a Cracked Heat Exchanger: 

• Furnace shuts off: A cracked heat exchanger may cause your furnace to turn 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 may smell like formaldehyde, are a significant warning sign. 
• Carbon monoxide alarm is triggered or you feel health problems: If a cracked heat exchanger is releasing carbon monoxide into your home, your carbon monoxide alarm could go off or family members may struggle with signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If the alarm goes off or you feel unusually tired, exit the home right away and then call for help. 
• Soot: If you notice black sooty accumulating near the exterior of your furnace, it’s an indication something may be seriously wrong.

What to Do if a Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, contact a professional experienced in furnace installation as soon as possible so they can inspect your system and, if necessary, handle a furnace heat exchanger replacement. Costs often fluctuate depending on the situation, but estimates run in the neighborhood of $1,000 to $3,000. 

Estimates aside, the good news is that heat exchangers are regularly covered by the warranty. You should check the warranty paperwork on your furnace, since while the warranty won't always cover the entire cost of repairs, it could significantly lower 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 provide the best possible return on investment when they work efficiently. Calling a certified professional to check your furnace for old parts, clogs in the air filters and other likely problems can help you avoid getting a big bill later on.  

It’s also beneficial 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 are not part of the heat exchanger itself, the strain of drawing air through a clogged filter makes your entire furnace work harder to do its job. And the harder your furnace works, the more deterioration components like the heat exchanger will endure.