Reviewed by Brian Gordon, President · Last Reviewed: September 30, 2026 · 2 min read
You'll find plenty of "if repair costs more than X% of a new system, replace it" rules online. They're a reasonable starting heuristic, but treating them as an absolute rule skips over the factors that actually matter for your specific situation.
Age isn't the whole story
Most residential AC systems last somewhere in the 12–15 year range with reasonable maintenance, and furnaces often run a bit longer. But a well-maintained 13-year-old system and a neglected 8-year-old system can be in very different real-world condition. Age is a useful data point, not a verdict on its own.
What actually belongs in the decision
- Repair cost relative to replacement cost. A minor repair on an older system is usually still worth doing. A major component failure — a compressor, a heat exchanger — on a system already past its typical service life is a different calculation.
- Repair frequency. One repair is normal wear. A second or third significant repair within a couple of years is a pattern, not bad luck.
- Refrigerant type. An older system using a phased-down refrigerant can face higher repair costs simply because sourcing that refrigerant is more limited — see our refrigerant transition article.
- Efficiency drift. Equipment loses some efficiency as it ages, even with maintenance. Rising bills without a clear cause is worth factoring in, though it shouldn't be the only reason to replace.
- How long you plan to stay. A repair that buys two more reliable years makes more sense for a homeowner planning to move soon than for someone settling in long-term.
- Comfort, not just function. A system that technically "still works" but never quite keeps up, runs constantly, or can't manage humidity is providing less value than the sticker price suggests.
What we won't do
We won't hand you a generic percentage formula and call it a recommendation. A repair-or-replace conversation should include a real look at your system's condition, its repair history if you have it, and what you actually want out of your next several years of ownership — not just an age cutoff.
Next step
If you're facing this decision right now, an in-person evaluation gives you a much more useful answer than any online formula — including this one.