VNA(Very Narrow Aisle) forklift trucks require narrower aisle width than traditional counter-balanced trucks do because only the fork assembly turns in the aisle instead of the entire body of the truck. Substituting the VNA trucks for the existing counter-balanced trucks will result in the significant increase of revenue due to the increased storage capacity in the distribution centers. In this study, we present an economic analysis model for the substitution, in which we present a closed-form equation for the number of racks to stay unmoved, while maximizing the additional storage capacity; and resulting payback period of the substitution. A case study shows the payback period of only 8.1 months, indicating that this substitution is very profitable.