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

One source might be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s critical to familiarize yourself with the signs of a cracked heat exchanger and what you can do if you believe that might be 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 system. It generally accomplishes this through coils or tubes that warm the air while functioning as a barrier to keep the gasses formed in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Given its key role, it’s no surprise that a broken heat exchanger can be very dangerous. Cracks in the heat exchanger can permit dangerous gasses – such as carbon monoxide, which can be lethal – to flow across your home. 

For this reason, don't ever turn on your heating if you suspect there's a crack in the heat exchanger, as this could make the entire family sick. Reach out to an HVAC professional as soon as possible if you think your furnace has a cracked heat exchanger that needs to be repaired. 

Four Symptoms of a Cracked Heat Exchanger: 

• Furnace switches off: Cracks in the heat exchanger may cause your furnace to shut off. 
• Odd Smells: If the air coming out of your furnace has an intense chemical scent, it might be evidence gas is slipping through cracks in your heat exchanger. These gasses, which can smell like formaldehyde, are a common warning sign. 
• Carbon monoxide alarm initiates or you notice health problems: If a cracked heat exchanger is emitting carbon monoxide inside your home, your carbon monoxide alarm should go off or family members might struggle with signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If your alarm goes off or you feel unusually tired, leave the home right away and then call for help. 
• Soot: If you notice black sooty collecting on the exterior of your furnace, it’s more evidence something might be seriously wrong.

What You Should Do if a Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, contact a pro with extensive experience in furnace installation right away so they can examine your system and, if required, start a furnace heat exchanger replacement. Costs should differ depending on the situation, but estimates run in the neighborhood of $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are generally protected by the warranty. You’ll want to review the warranty paperwork on your furnace, since while the warranty may not cover the entire cost of repairs, it still may significantly lower your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to minimize the risk of problems in your furnace overall is through regular furnace maintenance. Furnaces offer the most benefits when they operate efficiently. Hiring a skilled professional to inspect your furnace for old parts, clogs in the air filters and other potential problems can keep you from getting a big bill later on.  

It’s also helpful to take a look at your furnace filters every few months – it’s encouraged 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 pulling air through a clogged filter makes the entire furnace work more vigorously to complete its job. And the harder your furnace has to work, the more deterioration parts like the heat exchanger will experience.