A theoretical study for computing the effects of amplitude and wavelength of the wavy fin on the thermal performance of a single pass flat plate solar air heater is presented. A C++ program code with an iterative solution procedure has been developed to solve the governing energy equations and to evaluate the mean temperatures of the collector. The effect of mass flow rate, amplitude and wavelength variation of the wavy fin on the thermal and thermohydraulic performance of present solar air heater was investigated. For the entire range of mass flow and a constant value of amp = 0.75 cm, thermal and thermohydraulic efficiency decreases with increase in wavelength. Also, for constant value of wavelength = 7 cm, thermal efficiency increases with increase in amplitude whereas thermohydraulic efficiency increases up to the mass flow rate of 0.06 kg/s, beyond that thermohydraulic efficiency decreases. A comparison for the results of the present model is done with the plane solar air heater as well as the experimental results available in the literature. The results show a great enhancement in the thermal and thermohydraulic performance with the modified solar air heater. (C) 2017 Elsevier Ltd. All rights reserved.