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

One source could be that your furnace has a cracked heat exchanger. It can potentially be hazardous, so it’s critical to learn the signs of a cracked heat exchanger and what you can 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 flows inside the system. It usually accomplishes this via coils or tubes that heat the air while functioning as a barrier to keep the gasses created in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Thanks to its key role, it shouldn't come as a surprise that a cracked heat exchanger can be very dangerous. Cracks in the heat exchanger can permit dangerous gasses – including carbon monoxide, which can be lethal – to circulate through your home. 

For that reason, don't ever use your heater if you suspect there's a crack in the heat exchanger, as letting it run could make the entire family sick. Reach out to an HVAC professional immediately if you believe your heating has a cracked heat exchanger that needs repair. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: Cracks in the heat exchanger can cause your furnace to switch off. 
  • Unusual Smells: If the air escaping your furnace has a powerful chemical odor, it might be evidence gasses are seeping through cracks in your heat exchanger. These byproducts, which can smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm is triggered or you recognize health problems: If a cracked heat exchanger is releasing carbon monoxide in your home, your carbon monoxide alarm could go off or household members could experience signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling sleepy. If the alarm goes off or you feel unusually tired, leave the home immediately and then call for help. 
  • Soot: If you see black sooty collecting on the exterior of your furnace, it’s more evidence something might be seriously wrong.

What You Should Do if the Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, call a professional well versed in furnace installation as soon as possible so they can inspect your system and, if necessary, perform a furnace heat exchanger replacement. Costs will differ depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

However, the good news is that heat exchangers are generally protected by the warranty. You should check the warranty paperwork on your furnace, because while the warranty won't always cover the entire cost of repairs, it still may significantly shrink your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to prevent a problem in your furnace overall is via regular furnace maintenance. Furnaces provide the best possible return on investment when they run efficiently. Contacting a certified professional to examine your furnace for old parts, clogged filters and other common problems can keep you from getting a big bill later on.  

It’s also a good idea to take a look at your furnace filters every few months – it’s encouraged some filters be replaced 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 dragging air through a clogged filter makes your entire furnace work harder to complete its job. And the harder your furnace works, the more strain pieces like the heat exchanger will endure.