A furnace is usually a background player at home, ensuring you're warm in 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 can potentially be hazardous, so it’s critical to familiarize yourself with the signs of a cracked heat exchanger and what to do if you suspect that is 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 circulates inside the air ducts. It generally handles this through 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? 

Because of its central role, it isn't surprising that a broken heat exchanger can be very dangerous. A crack in the heat exchanger can permit dangerous gasses – such as carbon monoxide, which can be lethal – to flow throughout your home. 

For that reason, don't ever use your furnace if you believe there's a crack in the heat exchanger, as letting it run could make your entire household ill. Call an HVAC professional immediately if you believe your heater has a cracked heat exchanger that should be repaired. 

Four Symptoms of a Cracked Heat Exchanger: 

  • Furnace turns off: A crack in your heat exchanger could cause your furnace to shut off. 
  • Unusual Smells: If the air coming out of your furnace has a strong chemical scent, it might be evidence gasses are seeping through cracks in your heat exchanger. These gasses, which will often smell like formaldehyde, are a common warning sign. 
  • Carbon monoxide alarm initiates or you feel health problems: If a cracked heat exchanger is relieving carbon monoxide inside your home, your carbon monoxide alarm may go off or household members could struggle with signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If the alarm goes off or you feel unusually tired, get out of the home immediately and then call for help. 
  • Soot: If you spot black sooty accumulating around the exterior of your furnace, it’s more evidence something could be seriously wrong.

What You Should Do if the Furnace Heat Exchanger is Cracked 

If you believe your furnace has a cracked heat exchanger, contact a professional experienced in furnace installation right away so they can take a look at your system and, if required, perform a furnace heat exchanger replacement. Costs should fluctuate depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

However, the good news is that heat exchangers are generally included in the warranty. You’ll want to confirm the warranty paperwork on your furnace, since while the warranty might not 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 with routine furnace maintenance. Furnaces provide the best possible return on investment when they operate efficiently. Hiring a certified professional to examine your furnace for broken-down parts, dirty filters and other potential problems can keep you from getting a big bill later on.  

It’s also beneficial to review your furnace filters every few months – it’s ideal some filters be swapped out 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 the entire furnace work more vigorously to do its job. And the harder your furnace needs to run, the more strain parts like the heat exchanger will sustain.