There are two major reasons, Safety and Efficiency.
Having your furnace annually serviced is one way to help extend its life. When your furnace reaches 10-12 years, it is strongly recommended that you hire a licensed HVAC (Heating Ventilation-Air Conditioning) company to perform a heat exchanger inspection. This test should be performed annually from this point forward until the furnace is replaced. Why? Just as a piece of metal is bent over and over again eventually fatigues and breaks, a similar force is being exerted on your furnace's heat exchanger. During operation, the thin metal of the heat exchanger is being heated to high temperatures (sometimes over 175 degrees Fahrenheit) and cooled down to room temperature (70 degrees F). Each time, the metal expands as it warms up and contracts as it cools. Eventually, the metal fails and a crack is formed. A crack will always develop in a heat exchanger. How soon depends on the conditions it has been subjected to over its lifetime.
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