Commercial rooftop units, air handlers, and packaged systems are typically designed for a 15–20 year service life under normal operating conditions. In Wisconsin's climate — where HVAC systems run aggressively for both heating and cooling seasons — that lifespan is often on the shorter end of that range.

Age alone isn't always a reason to replace. A well-maintained 18-year-old RTU that runs efficiently and hasn't required significant repairs may have more life ahead of it. But age is the context that makes every other sign on this list more significant. A repair that would be a routine expense on a 7-year-old system becomes a harder financial case on a system approaching the end of its expected life.

A widely used industry benchmark is this: if the cost of a repair exceeds 50% of the cost of replacing the equipment, replacement is generally the better financial decision. The logic is straightforward — you're spending a significant portion of the replacement cost to extend the life of aging equipment that will likely need another major repair within a few years.

For a commercial RTU with a current replacement value of $18,000, a $9,000 compressor repair sits right at that threshold. For most facility managers, that's the moment to have a serious replacement conversation rather than authorize the repair and revisit the same decision in 18 months.

The 50% rule becomes even more compelling when the system has a history of recurring repairs. One major repair is an event. A pattern of repairs is a trend — and trends don't reverse themselves on aging commercial equipment.

Commercial HVAC systems lose efficiency gradually and consistently as they age. Heat transfer surfaces accumulate fouling. Compressor efficiency declines. Economizers that once modulated freely become stuck. Controls drift from their original calibration. None of these changes are dramatic individually, but together they produce a system that consumes meaningfully more energy to deliver the same conditioning it once provided efficiently.

If your energy costs have trended upward over two or three years — without a corresponding increase in operating hours, building square footage, or process loads — aging HVAC equipment is a likely contributor. A system that was SEER 10 when installed may be operating at the equivalent of SEER 6 or lower today. Modern replacement equipment at SEER 16–18 can reduce cooling energy consumption by 30–40% compared to degraded older equipment.

R-22 refrigerant — common in commercial HVAC equipment manufactured before 2010 — was phased out of production in the United States under EPA regulations. It is no longer manufactured domestically, and the remaining supply consists of reclaimed or imported stockpiles that are dwindling and increasingly expensive.

If your equipment requires R-22 and develops a refrigerant leak, you're facing a compounding problem: the cost of the repair, plus the cost of R-22 at current market prices, plus the near certainty that the same leak or another will occur again. There is no long-term path forward for R-22 equipment — the refrigerant will only become harder and more expensive to source with each passing year.

Persistent comfort complaints — zones that can't maintain setpoint, areas that overheat in summer or can't hold temperature in winter, humidity problems that didn't exist before — are often dismissed as occupant preference issues. In many cases, they're equipment performance issues that a service call won't resolve.

A system that once balanced a 40,000 sq ft facility adequately may no longer have the capacity or control authority to do so reliably. VAV terminal units that aren't sequencing properly because the BAS hasn't been recommissioned in years. RTUs that cycle erratically because their controls have drifted. Supply air temperatures that swing outside design range because heat transfer surfaces are fouled.

If complaints are concentrated in certain zones and have persisted across multiple service visits without resolution, the problem is likely systemic — a sign that the equipment can no longer deliver what the building requires.

Buildings change. Occupancy increases. Process equipment is added. Office space is converted to server rooms. A building that was adequately conditioned by its original HVAC system five years ago may now be asking more of that system than it was designed to deliver — and an aging system with diminished capacity is the worst position from which to meet increased demand.

Signs that your system is undersized for current loads include supply air temperatures at or above setpoint during peak conditions, equipment running at 100% capacity without satisfying the building, and thermostats that simply cannot be maintained at design conditions even with no apparent equipment fault.

A proper load calculation — part of any commercial HVAC engineering engagement — will tell you exactly what your building requires and whether your current equipment can provide it. If the answer is no, replacement isn't just preferable — it's the only path to reliable performance.

Manufacturers support their equipment with replacement parts for a defined period after discontinuing a product line. Once that support period ends, parts availability moves to third-party suppliers and reclaimed inventory — which is variable, often expensive, and eventually exhausted.

When your service technician begins telling you that a needed part has a six-week lead time, requires sourcing from a specialty supplier, or is simply no longer available, you're approaching the end of your equipment's maintainable life. A system you can't get parts for is a system you can't keep running — and the longer you defer replacement, the higher the probability of a breakdown during a critical period when you have no good options.