What Is the Average Lifetime of a Furnace Heat Exchanger?

Symptoms

• Rust marks on a furnace can indicate that you have a cracked heat exchanger, because heat exchangers are prone to problems if your furnace is exposed to wet conditions, or if water from a plumbing leak drips onto the heat exchanger. If you have a gas furnace, you can look for evidence of a cracked heat exchanger by examining the color and pattern of the flame when the blower turns on. If the flame changes color, or wavers and jumps when the blower turns on, the heat exchanger might be damaged.

Inspecting

• Several tests can be performed to check your heat exchanger for cracks. A visual inspection may find some damage, but because only 20 percent of the heat exchanger is visible, you shouldn’t rely solely on a visual inspection. Using a telescoping mirror and flashlight will allow you to see more. The appearance of discolored metal or soot in the heat exchanger also indicate that it’s cracked. One common test involves placing a smoke bomb inside the heat exchanger and watching to see if smoke escapes into the plenum chamber.

Early Cracking

• A dirty air filter, fan or ductwork reduces the flow of air in your furnace, causing it to overheat. The temperature rise caused by dirt and dust isn’t usually enough to shut the furnace down but, over time, it causes metal fatigue that can lead to early cracking of your heat exchanger. Rust build-up also shortens the life of heat exchangers. Rust problems are more severe when chlorinated compounds found in detergents, bleach and other household products combine with water to form hydrochloric acid. This acid corrodes the furnace and ruins the heat exchanger. Heat exchangers can also crack prematurely when they’re damaged or dropped during shipping or installation, or if they have manufacturing defects.

Extending the Lifespan of your Furnace

• Cleaning and maintaining your furnace will extend the lifespan of your heat exchanger. Ensure a good flow of air by changing the furnace filter whenever it gets dirty. Inspect the air vents and ductwork for blockages and keep them clean. Cleaning the fan blades and motor will make your furnace more efficient and help ensure that your heat exchanger doesn’t crack prematurely.

Repairing or Replacing Heat Exchangers

• Heat exchangers can be replaced on many furnaces, though not on certain old furnaces, on which it's an integral part. Accordingly, it may not be possible to find a heat exchanger if your furnace is 20 years old or older. Because the heat exchanger is the most expensive part of the furnace, it’s also not always cost effective to replace them on furnaces that are 10 years old or older. Purchasing a new, higher efficiency furnace may be a better choice.