Two solutions are obtained for the optimal size of a biomass utilization facility subject to an economy of scale in capital and non-fuel operating costs. The conventional assumption of constant-scaling parameter over all capacities leads to a larger optimum than if the scaling factor is increased asymptotically towards with increasing capacity to reflect technical and economic constraints or risks. Lack of appropriate scaling data for larger sizes makes the question of general optimization for biomass facilities uncertain. and conclusions regarding development policies based on assumptions of constant cost scaling should be carefully tested.