A furnace is usually a background player at home, ensuring you're warm across the cold winter months. It regularly isn't noticed until a malfunction appears. 

One source might be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s important to learn the evidence of a cracked heat exchanger and what you should do if you believe that might 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 flows inside the ventilation. It usually does this via coils or tubes that heat the air while acting as a barrier to keep gas formed in the combustion chamber, called flue gasses, from leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its central role, it’s no surprise that a damaged heat exchanger can be very dangerous. A damaged heat exchanger can permit dangerous gasses – like carbon monoxide, which can be lethal – to flow throughout your home. 

For obvious reasons, do NOT run your heating if you believe you're dealing with a cracked heat exchanger, as this could make the whole family sick. Reach out to an HVAC professional as soon as possible if you are worried your heating has a cracked heat exchanger that should be repaired. 

Four Signs of a Cracked Heat Exchanger: 

• Furnace switches off: Cracks in the heat exchanger can cause your furnace to turn off. 
• Odd Smells: If the air leaving your furnace has an intense chemical scent, it could be an indicator that gas is leaking through cracks in your heat exchanger. These gasses, which may smell like formaldehyde, are a major warning sign. 
• Carbon monoxide alarm goes off or you feel symptoms of poisoning: If a cracked heat exchanger is relieving carbon monoxide inside your home, your carbon monoxide alarm may go off or household members might 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 sick, get out of the home immediately and then call for help. 
• Soot: If you spot black sooty collecting around the exterior of your furnace, it’s another sign something may be seriously wrong.

What to Do if the Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, hire a professional with extensive experience in furnace installation right away so they can take a look at your system and, if needed, start a furnace heat exchanger replacement. Costs will differ depending on the situation, but estimates run in the neighborhood of $1,000 to $3,000. 

However, the good news is that heat exchangers are generally covered by 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 could significantly lower your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the easiest ways to prevent a problem in your furnace overall is via consistent furnace maintenance. Furnaces work the best when they operate efficiently. Calling a trained professional to inspect your furnace for worn-out parts, dirty filters and other common problems can help you avoid 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 pulling air through a clogged filter makes your entire furnace work more vigorously to accomplish its job. And the harder your furnace works, the more deterioration parts like the heat exchanger will sustain.