A furnace is usually a background player at home, keeping you warm during the cold winter months. It frequently won't be noticed until something goes wrong. 

One cause could be that your furnace has a cracked heat exchanger. It’s a potentially dangerous issue, so it’s important to familiarize yourself with 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 transition heat from the combustion chamber inside your furnace to the air that moves inside the air ducts. It generally handles this with coils or tubes that warm the air while serving as a barrier to keep byproducts created in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its important role, it isn't surprising that a broken heat exchanger can be very dangerous. A damaged heat exchanger can enable dangerous gasses – including carbon monoxide, which can be lethal – to circulate across your home. 

For that reason, do NOT use your heater if you suspect it has a cracked heat exchanger, as doing so could make the whole household ill. Contact an HVAC professional right away if you are worried your furnace has a cracked heat exchanger that needs to be repaired. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: Cracks in the heat exchanger can cause your furnace to turn off. 
  • Unusual Smells: If the air coming out of your furnace has a strong chemical smell, it may be evidence gasses are leaking through cracks in your heat exchanger. These byproducts, which will often smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm goes off or you recognize poisoning symptoms: If a cracked heat exchanger is emitting carbon monoxide into your home, your carbon monoxide alarm could go off or family members might start experiencing signs of carbon monoxide poisoning. Symptoms include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If your alarm goes off or you feel unwell, exit the home right away and then call for help. 
  • Soot: If you find black sooty buildup near the exterior of your furnace, it’s another sign something might be seriously wrong.

What You Can Do if a Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, call a professional experienced in furnace installation Phoenix as soon as possible so they can inspect your system and, if needed, start a furnace heat exchanger replacement. Costs will fluctuate depending on the situation, but estimates can roughly suggest $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, as while the warranty might not cover the entire cost of repairs, it could significantly lower your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the easiest ways to prevent a problem in your furnace overall is through consistent furnace maintenance. Furnaces provide the best possible return on investment when they operate efficiently. Hiring a trained professional to examine your furnace for broken-down parts, clogged filters and other common problems can keep you from getting a big bill later on.  

It’s also helpful to inspect your furnace filters every few months – it’s encouraged some filters be swapped out 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 drawing air through a clogged filter makes your entire furnace work longer to do its job. And the harder your furnace has to work, the more strain components like the heat exchanger will endure.