A furnace is almost always a background player in your home, helping keep you warm during the cold winter months. It regularly doesn’t get noticed until a malfunction appears. 

One cause may be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s important to learn the signs of a cracked heat exchanger and what to do if you are worried that may 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 through the ventilation. It typically does this using coils or tubes that heat the air while acting 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 key role, it shouldn't come as a surprise that a damaged heat exchanger can be very dangerous. A crack in the heat exchanger can enable dangerous gasses – such as carbon monoxide, which can be lethal – to be distributed through your home. 

For this reason, do NOT turn on your heating if you think there's a crack in the heat exchanger, as doing so could make the whole family sick. Reach out to an HVAC professional immediately if you believe your heater has a cracked heat exchanger that needs repair. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace shuts off: A cracked heat exchanger may cause your furnace to switch off. 
  • Strange Smells: If the air escaping your furnace has a powerful chemical scent, it might be a sign gas is seeping through cracks in your heat exchanger. These gasses, which will often smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm is triggered or you notice symptoms of poisoning: If a cracked heat exchanger is emitting carbon monoxide inside your home, your carbon monoxide alarm should go off or household members could start experiencing signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If an alarm goes off or you feel unwell, leave the home immediately and then call for help. 
  • Soot: If you spot black sooty accumulating near the exterior of your furnace, it’s more evidence something might be seriously wrong.

What to Do if the Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, call a pro experienced in furnace installation as soon as possible so they can inspect your system and, if needed, perform a furnace heat exchanger replacement. Costs will vary depending on the situation, but estimates often hover around $1,000 to $3,000. 

Estimates aside, the good news is that heat exchangers are regularly protected by the warranty. It's a good idea to confirm the warranty paperwork on your furnace, because while the warranty won't always cover the entire cost of repairs, it still may significantly lower your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the easiest 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 work efficiently. Contacting a certified 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 a good idea to review your furnace filters every few months – it’s ideal 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 the entire furnace work longer to complete its job. And the harder your furnace works, the more strain components like the heat exchanger will endure.