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How long does a furnace last?

A gas furnace typically lasts 15 to 20 years. Electric furnaces often last a little longer because they have fewer parts that wear out. The first step is to find out how old yours is: decode the serial number.

Signs a furnace is near the end

• It is over 15 years old and needing repairs more than once a season.
• Heating bills rising without a change in use.
• Uneven heat, short cycling, or the blower running much longer than it used to.
• A yellow, flickering burner flame instead of a steady blue one, soot, or a carbon monoxide alarm. Turn it off and call a technician.
• Rust or cracks on the heat exchanger, found during a service visit.

Repair or replace?

A common rule of thumb: multiply the furnace's age by the repair cost. If the result is over about $5,000, or the repair costs more than a third of a new furnace, replacing it usually makes more sense. Furnaces made before 1992 were built before the federal 78% efficiency minimum, so replacing one with a modern 95% furnace also cuts fuel use.