A furnace is usually a background player for your home, ensuring you're warm across the cold winter months. It frequently won't be noticed until something goes wrong. 

One root cause could be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s important to know the symptoms of a cracked heat exchanger and what to do if you are worried that might be the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger helps move heat from the combustion chamber of your furnace to the air that moves throughout the ventilation. It usually does this using coils or tubes that heat up the air while functioning as a barrier to keep gas created 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 be hazardous. Cracks in the heat exchanger can allow dangerous gasses – including carbon monoxide, which can be lethal – to flow throughout your home. 

For obvious reasons, do NOT turn on your heating if you believe you're dealing with a cracked heat exchanger, as doing so could make your entire household ill. Reach out to an HVAC professional as soon as possible if you think your heater has a cracked heat exchanger that needs repair. 

Four Signs of a Cracked Heat Exchanger: 

• Furnace shuts off: Cracks in the heat exchanger may cause your furnace to switch off. 
• Odd Smells: If the air coming out of your furnace has a powerful chemical smell, it may be a sign gas is slipping through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a common warning sign. 
• Carbon monoxide alarm initiates 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 may start experiencing signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If an alarm goes off or you feel sick, get out of the home immediately and then call for help. 
• Soot: If you notice black sooty buildup around the exterior of your furnace, it’s an indication something may be seriously wrong.

What You Can Do if a Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, call a professional with extensive experience in furnace installation right away so they can inspect your system and, if necessary, perform a furnace heat exchanger replacement. Costs should fluctuate depending on the situation, but estimates often hover around $1,000 to $3,000. 

Fortunately, the good news is that heat exchangers are generally covered by the warranty. You should review the warranty paperwork on your furnace, since while the warranty might not cover the entire cost of repairs, it can significantly shrink your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the best ways to minimize the risk of problems in your furnace overall is via regular furnace maintenance. Furnaces provide the best possible return on investment when they run efficiently. Calling a trained professional to check your furnace for broken-down 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 ideal some filters be changed every 90 days or sooner if they are dirty or grimy. While the filters aren't connected to the heat exchanger itself, the strain of pulling air through a clogged filter makes the entire furnace work harder to do its job. And the harder your furnace works, the more strain parts like the heat exchanger will sustain.