In this work, natural convection heat transfer in horizontally oriented, vertical sinusoidal wavy fins, involving radiation heat transfer were investigated experimentally. Experiments were done with wavy fins having three different amplitudes, namely H/30, H/15 and H/10, with different heater power inputs. Results were compared to the results of a rectangular finned plate and also a reference horizontal base plate. Power of the heater was changed from 1.02 W to a maximum of 32.06 W and totally 69 experiments were done for 5 test sets. Results indicate that, heat transfer enhancement is better with wavy fins than with the rectangular fins. On the other hand, after a certain value of the wave amplitude the increase in the amplitude negatively affecting the natural convection due to the blockage of fluid motion. The results also indicate that, an important part of total heat transfer is by radiation and should be considered in natural convection studies of finned surface heat sinks. (C) 2019 Elsevier Ltd. All rights reserved.