When to repair your furnace and when to replace it
Age, repair cost, and how often the furnace has needed work all feed into the decision together. An old unit with a steep repair bill and a pattern of recent problems points toward replacement. A younger unit with its first repair, even a costly one, usually points the other way.
How do you decide to repair or replace a furnace?
Three variables drive the decision, and none of them works alone.
The first is age. A furnace deep into its expected lifespan carries a different risk profile than one still in its earlier years, because the parts that fail next are likely to be as worn as the part that just failed. The second is repair cost relative to replacement cost. A small repair on an old unit can still make sense; a large one rarely does. The third is failure history. A furnace having its first problem sits in a different position than one that has needed work repeatedly in a short window. Where your furnace lands on all three of those variables together is what shapes the answer, because a single bad variable does not automatically tip the scale the way two or three compounding ones do.
When the symptom could be something worse
The cost-versus-age framework works when the problem is known.
A failed ignitor, a worn blower motor, a cracked inducer housing: these are diagnosable from a description and priceable before anyone opens the unit. Some failure types break that model entirely. A cracked heat exchanger produces symptoms that look like a dozen cheaper problems. Carbon monoxide readings, combustion analysis, and physical inspection with the right equipment are the only way to rule it out. Sizing is the same kind of problem. A furnace that runs constantly but cannot hold temperature could be undersized for the house, or it could be a heat exchanger or duct issue that has gone undiagnosed for years. You cannot tell the difference by watching it run. At that point, the earlier framework does not apply yet, because the diagnosis itself is what a professional needs to deliver first.
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