A furnace is often a background player at home, ensuring you're warm during the cold winter months. It often doesn’t get noticed until something goes wrong. 

One source may be that your furnace has a cracked heat exchanger. It can be a safety risk, so it’s important to familiarize yourself with the evidence of a cracked heat exchanger and what you can 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 moves inside the ventilation. It usually accomplishes this using coils or tubes that warm the air while acting as a barrier to keep the gasses produced in the combustion chamber, called flue gasses, from escaping out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

Given its central role, it’s no surprise that a cracked heat exchanger can pose a risk. A damaged heat exchanger can allow dangerous gasses – including carbon monoxide, which can be lethal – to circulate through your home. 

For obvious reasons, never use your heater if you suspect you're dealing with a cracked heat exchanger, as letting it run could make the entire family ill. Call an HVAC professional immediately if you are worried your furnace has a cracked heat exchanger that should be repaired. 

Four Signs of a Cracked Heat Exchanger: 

  • Furnace turns off: Cracks in the heat exchanger could cause your furnace to switch off. 
  • Strange Smells: If the air coming out of your furnace has a powerful chemical odor, it may be evidence gas is slipping through cracks in your heat exchanger. These byproducts, which will often smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm goes off or you recognize health problems: If a cracked heat exchanger is releasing carbon monoxide inside your home, your carbon monoxide alarm could go off or family members might struggle with signs of carbon monoxide poisoning. Side effects include headaches, dizziness, weakness, nausea, vomiting or feeling tired. If an alarm goes off or you feel sick, get out of the home as soon as you can and then call for help. 
  • Soot: If you find black sooty buildup on the exterior of your furnace, it’s more evidence something may be seriously wrong.

What You Should Do if Your Furnace Heat Exchanger is Cracked 

If you suspect your furnace has a cracked heat exchanger, call a professional with extensive experience in furnace installation as soon as possible so they can take a look at your system and, if necessary, start 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 included in the warranty. It's a good idea to confirm the warranty paperwork on your furnace, as while the warranty won't always cover the entire cost of repairs, it could significantly shrink your bill.  

How to Avoid a Cracked Heat Exchanger in Your Home  

One of the easiest ways to avoid problems in your furnace overall is with routine furnace maintenance. Furnaces provide the best possible return on investment when they work efficiently. Calling a trained professional to inspect your furnace for old parts, clogged filters and other likely problems can help you avoid getting a big bill later on.  

It’s also helpful to take a look at your furnace filters every few months – it’s recommended 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 dragging air through a clogged filter makes the entire furnace work more vigorously to accomplish its job. And the harder your furnace needs to run, the more deterioration pieces like the heat exchanger will experience.