A furnace is often a background player at home, keeping you warm in the cold winter months. It frequently doesn’t get noticed until a malfunction appears. 

One source may 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 you should do if you are worried that may be 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 moves throughout the ventilation. It usually handles this with coils or tubes that warm the air while functioning as a barrier to keep byproducts created in the combustion chamber, called flue gasses, from leaking out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Because of its key role, it’s no surprise that a broken heat exchanger can be hazardous. A damaged heat exchanger can enable dangerous gasses – such as carbon monoxide, which can be lethal – to flow through your home. 

For that reason, do NOT run your heating if you think it has a cracked heat exchanger, as doing so could make your entire family ill. Reach out to an HVAC professional as soon as possible if you think your heater has a cracked heat exchanger that should be repaired. 

Four Warning Signs of a Cracked Heat Exchanger: 

  • Furnace switches off: A crack in your heat exchanger can cause your furnace to turn off. 
  • Unusual Smells: If the air escaping your furnace has a strong chemical scent, it might be a sign gas is seeping through cracks in your heat exchanger. These gasses, which may smell like formaldehyde, are a significant warning sign. 
  • Carbon monoxide alarm goes off or you feel poisoning symptoms: If a cracked heat exchanger is relieving carbon monoxide inside your home, your carbon monoxide alarm should go off or family members could experience 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, leave the home immediately and then call for help. 
  • Soot: If you find black sooty accumulating on the exterior of your furnace, it’s an indication something might be seriously wrong.

What You Can Do if Your Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, hire a professional well versed in furnace installation as soon as possible so they can inspect your system and, if needed, perform a furnace heat exchanger replacement. Costs should differ depending on the situation, but estimates often hover around $1,000 to $3,000. 

Estimates aside, the good news is that heat exchangers are often protected by the warranty. You should confirm the warranty paperwork on your furnace, because while the warranty might not cover the entire cost of repairs, it can significantly reduce your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the most convenient ways to avoid problems in your furnace overall is through consistent furnace maintenance. Furnaces offer the most benefits when they work efficiently. Contacting a certified professional to inspect your furnace for broken-down parts, clogged filters and other potential problems can keep you from getting a big bill later on.  

It’s also helpful to review your furnace filters every few months – it’s recommended 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 complete its job. And the harder your furnace needs to run, the more strain components like the heat exchanger will sustain.