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

One cause could be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s worthwhile to learn the evidence of a cracked heat exchanger and what to do if you believe that is the problem.  

What Is a Heat Exchanger in a Furnace? 

A heat exchanger transfers heat from the combustion chamber inside your furnace to the air that flows through the system. It typically does this via coils or tubes that heat up the air while serving as a barrier to keep gas created in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Given its important role, it’s no surprise that a damaged heat exchanger can be hazardous. A crack in the heat exchanger can enable dangerous gasses – such as carbon monoxide, which can be lethal – to flow across your home. 

For obvious reasons, don't ever run your heating if you suspect it has a cracked heat exchanger, as doing so could make the whole family ill. Contact an HVAC professional as soon as possible if you are worried your heater has a cracked heat exchanger that should be repaired. 

Four Symptoms of a Cracked Heat Exchanger: 

• Furnace shuts off: A cracked heat exchanger could cause your furnace to switch off. 
• Unusual Smells: If the air leaving your furnace has a strong chemical smell, it might be evidence gasses are slipping through cracks in your heat exchanger. These byproducts, which can smell like formaldehyde, are a common warning sign. 
• Carbon monoxide alarm goes off or you recognize symptoms of poisoning: If a cracked heat exchanger is releasing carbon monoxide inside your home, your carbon monoxide alarm may go off or family members may start experiencing signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If an alarm goes off or you feel unusually tired, exit the home as soon as you can and then call for help. 
• Soot: If you notice black sooty collecting around the exterior of your furnace, it’s an indication something could be seriously wrong.

What to Do if a Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, contact a pro experienced in furnace installation right away so they can take a look at your system and, if required, handle a furnace heat exchanger replacement. Costs will vary 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 included in the warranty. You should confirm the warranty paperwork on your furnace, since while the warranty may not cover the entire cost of repairs, it still may significantly reduce 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 via consistent furnace maintenance. Furnaces work the best when they operate efficiently. Calling a trained professional to examine your furnace for old parts, clogged filters and other potential problems can keep you from 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 aren't a part of the heat exchanger itself, the strain of dragging air through a clogged filter makes the entire furnace work harder to complete its job. And the harder your furnace has to work, the more wear and tear pieces like the heat exchanger will experience.