A furnace is usually a background player at home, keeping you warm across the cold winter months. It frequently 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 worthwhile to familiarize yourself with the signs of a cracked heat exchanger and what you can do if you believe 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 throughout the system. It generally accomplishes this through coils or tubes that heat up the air while acting as a barrier to keep gas formed in the combustion chamber, called flue gasses, from getting out into your home.  

Is a Cracked Heat Exchanger Dangerous? 

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

For this reason, don't ever run your heater if you believe you're dealing with a cracked heat exchanger, as doing so could make your entire household ill. Call an HVAC professional as soon as possible 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 leaving your furnace has an intense chemical smell, it may be evidence gasses are leaking through cracks in your heat exchanger. These byproducts, which may smell like formaldehyde, are a major warning sign. 
  • Carbon monoxide alarm initiates or you notice health problems: If a cracked heat exchanger is relieving carbon monoxide in your home, your carbon monoxide alarm should go off or family members may struggle with signs of carbon monoxide poisoning. Complications include headaches, dizziness, weakness, nausea, vomiting or feeling drowsy. If your alarm goes off or you feel sick, exit the home right away and then call for help. 
  • Soot: If you spot black sooty collecting near the exterior of your furnace, it’s another sign something might be seriously wrong.

What You Should Do if the Furnace Heat Exchanger is Cracked 

If you worry your furnace has a cracked heat exchanger, call a professional experienced in furnace installation right away so they can inspect your system and, if needed, perform a furnace heat exchanger replacement. Costs should differ depending on the situation, but estimates can roughly suggest $1,000 to $3,000. 

Estimates aside, the good news is that heat exchangers are often included in the warranty. You’ll want to confirm the warranty paperwork on your furnace, because while the warranty might not cover the entire cost of repairs, it can significantly lower your bill.  

How to Prevent a Cracked Heat Exchanger in Your Home  

One of the best ways to avoid problems in your furnace overall is with regular furnace maintenance. Furnaces offer the most benefits when they work efficiently. Calling a trained professional to inspect your furnace for old parts, dirty filters and other common problems can help you avoid 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 pulling air through a clogged filter makes your entire furnace work longer to complete its job. And the harder your furnace has to work, the more deterioration pieces like the heat exchanger will experience.