Ask Angie: When to replace a furnace

angieslist.comMarch 21, 2014 


Angie Hicks


Dear Angie: How do you know when it's time to replace a furnace? — Susan T., San Francisco

Dear Susan: I hope your furnace is getting a well-deserved rest after this freakishly frigid winter. You ask a great question: How can you be sure an older-but-operable unit can handle another heating season?

Highly rated HVAC experts tell our team that you should consider three factors before deciding whether it's time to invest $2,500 to $5,500 in a new furnace:

Age: A furnace has an average life span of 12 to 18 years, so if yours has been warming you for at least a dozen years, it might be time to consider replacement.

Energy efficiency: Outdated furnaces generally use more energy than new models. Also, an older unit might be oversize, which can cause it to "short cycle," or turn on and off more often than needed. Upgrading to a newer, smaller furnace might reduce your energy bills and increase your comfort level.

Problem signs: Signals that your furnace might need either a pro's attention or replacement include unusually high utility bills, rooms heating unevenly or a screeching or squealing noise, which might indicate a problem with the blower motor.

When considering whether it's worth it to invest in a repair, remember this rule of thumb: If a repair will cost more than half the price of a new appliance and the unit is more than six or seven years old, it's probably best to buy new.

If you decide to shop for a new unit, consider its "annual fuel utilization efficiency" number. AFUE is a measure of how efficiently a furnace converts fuel energy to heat over a typical year. A unit with an AFUE of 95 percent means that 95 percent of the fuel it burns becomes heat and the other 5 percent is lost. The higher the AFUE, the more efficient the furnace.

Angie Hicks compiles the best advice from the most highly rated service pros on to answer your questions. Ask Angie your question at

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