Life Span of a Furnace's Heat Exchanger

Damage

• Damage to heat exchangers can occur in several places. The wall may thin to less than half of its original thickness. Cracks can develop at various locations. Seams may open. Seals and gaskets may leak or holes can appear. Some cracks may only open when the furnace blower is running, so they can be hard to detect. Years of constant heating and cooling will cause all heat exchangers to crack or develop holes, but some heat exchangers crack prematurely.

Premature Cracks

• Premature cracking can occur if dirty filters aren’t changed or there’s dirt in the air vent or duct work and your furnace has to work too hard. It can also happen if the burners aren’t firing correctly, if the fan limit switch isn’t working or if condensation builds up in the heat exchanger, causing it to rust. Exposure to chlorinated compounds such as bleach, paint thinners or solvents can also cause abnormal rusting. Heat exchangers that are dropped or otherwise damaged during shipping or installation may also fail prematurely.

Inspection

• Sometimes you can see cracks in the heat exchanger by looking at it. However, since only 20 percent of the total surface of the heat exchanger is visible, you shouldn’t rely on a visual inspection to tell you whether your heat exchanger is all right. If you have a gas furnace, you can examine the flame at the burner for changes in color or pattern when the blower fan turns on. Changes in color or flames that jump or waver indicate that the heat exchanger has been damaged. A telescoping mirror and flashlight can be used to inspect heat exchangers on oil-fired furnaces. A qualified technician can run other tests, such as a water spray test, penetrating dye test or pressure change test.

Prolonging Life

• There are several ways to prolong the life of your furnace’s heat exchanger, beginning with an annual furnace inspection. Check the filter every month, and clean or change it if necessary. Use a soft cloth or a vacuum to clean the blower fan and blower housing. Vacuum dust from the draft hood. Keep the furnace area dry to reduce moisture that contributes to rust.

Known Problems

• Some furnaces and heat exchangers have known problems or frequent problems. The Consumer Products Safety Commission announces recalls of defective products when they pose a danger to consumers. One large recall involving more than 30,000 furnaces with burner and heat exchanger problems was settled in 2009. The furnaces, which were manufactured by Consolidated Industries, were sold under a variety of names. Some furnaces involved in the lawsuit are still being used today. According to the Consumer Products Safety Commission, there’s no end date to a product recall.