In this paper, the details of a numerical study performed for the optimum fin arrangement in a solar air heater with a rectangular fin array attached to the bottom side of the absorber plate have been presented. Results have been presented for various fin sizes and spacing between the fins, while the heat transfer and fluid flow are directed by natural convection. An inclined rectangular channel similar to the dimensions of a typical solar air heater has been considered. Three different fin configurations, namely, continuous long fins for the whole length of the channel, in-line interrupted and staggered interrupted arrangements of fins, have been studied. The present analysis aims to identify the optimum configuration of the fin array for enhanced heat transfer. The spacing between the fins and the height of the fins are varied to obtain an optimum configuration. The numerical simulations are performed for heat flux (q″) ranging from 250 to 750 W/m2 on the absorber plate. The inclination angles of the channel (θ) have been maintained at 15 deg, 30 deg, and 45 deg from the horizontal plane. The results show that with the spacing between fins, S = 5.4 cm performs better in the case of longitudinal continuous fin arrangement. However, a fin spacing of 4.75 cm shows a higher heat transfer in the case of staggered fin configuration. In comparison with nine long uninterrupted fins, using the staggered arrangement with 15 × 10 fins saves up to 33% of fin material.