At some point, every building owner has the same conversation with their HVAC contractor.
The system is struggling. A repair is possible but not cheap. The unit is old enough that another problem is probably coming. The contractor recommends replacement. The building owner does not know if that is the right call or a convenient upsell. Both outcomes are possible and they have seen both before.
The repair-versus-replace decision does not have to be a gut call. There are four variables that, taken together, almost always point in a clear direction. Here is how to run them before that conversation happens.
Start With the 50 Percent Rule
The most widely used benchmark in commercial HVAC: if the cost of the repair exceeds 50 percent of the cost of replacement, replace it.
A repair at that cost is buying you a partially repaired old system, with every other component still at whatever age and condition they were at before. You are spending significant money to extend the life of an asset that is already past its prime, with no guarantee the next failure is not six months out.
The 50 percent rule is a threshold, not a mandate. A unit that crosses it is a replacement candidate. Whether you actually replace it depends on what comes next.
Age Shifts the Probability
A commercial rooftop unit (RTU) under a disciplined maintenance program has a realistic life of 15 to 20 years. Under reactive-only maintenance, that drops to 8 to 12. Age matters to the repair-versus-replace decision because it changes the probability of future failures. A repair on a 7-year-old unit with a clean maintenance history is a different bet than the same repair on a 17-year-old unit with spotty records. The 7-year-old unit, properly repaired, has a reasonable runway ahead of it. The 17-year-old unit is a collection of aging components where the compressor, heat exchanger, capacitors, contactors, and belts are all approaching end of life around the same time. Repairing one of them does not change the math on the others. A repair on an older system often buys you 12 to 18 months, not a resolution.
Run the Energy Numbers
According to the U.S. Department of Energy's Advanced RTU Campaign, replacing older commercial rooftop units with modern high-efficiency units typically reduces energy use by 20 to 50 percent. In Michigan, where commercial buildings run hard through both heating and cooling seasons across a 100-degree annual swing, that gap is a real monthly number, not an engineering abstraction.
If your current unit is running $2,000 a month in attributable energy costs and a modern replacement cuts that by 25 percent, you are recovering $6,000 a year in savings. Add available rebates from DTE Energy or Consumers Energy and the payback period on a replacement can be shorter than most owners expect. The repair cost is a one-time number. The efficiency gap is a monthly number that compounds over the remaining life of the asset. Both belong in the decision.
Price In the Failure Scenario
Here is the factor that rarely gets named in the repair-versus-replace conversation: what does it cost if you repair the unit and it fails anyway in eight months?
You will have paid for the repair, plus an emergency response, plus the downstream costs of unplanned downtime. Portable cooling rentals. Tenant disruption. Expedited parts at peak-season rates. A planned replacement on your timeline eliminates that exposure entirely. Include the probability-weighted cost of the failure scenario when you are running the numbers. A repair that looks right in isolation looks different when you account for what happens if it does not hold.
Three Scenarios, Three Answers
Under 10 years old, documented maintenance history, repair cost well below 50 percent: repair it, and use the visit to assess everything else on the roof.
12 to 15 years old, inconsistent records, repair cost at or near the 50 percent threshold: start the replacement planning conversation now. Fix it if you need to maintain continuity, but budget for what is coming.
15 years or older, any maintenance history, major repair needed: replace it. The economics are not close once you factor in efficiency, remaining life, and failure risk. We are not going to tell every building owner to replace their equipment. We are going to tell you where yours actually stands, show you the numbers, and let you make the call. If you are not getting that conversation from your contractor, find one who will have it.
maintenance plans, 24/7 service, and system replacement across Southeast Michigan. Call (248) 590-0010 or reach out at sales@vitalitymechanical.com.