Air-side economizers are commonly used in most locations to reduce the cooling load when outdoor conditions are suitable. However, several field studies have shown that economizer faults, such as a stuck damper, are quite common. For small rooftop units, the cost of supplying an economizer can return a slow payback in some locations, and when faults occur, the economizer may not ever pay off. This study simulated the cost outcome using probabilities of faults from field studies to examine the cost-effectiveness of economizers for typical buildings in several climates, to determine payback period, if any.