This paper presents a numerical simulation of heat transfer in falling film flow over vertical walls. The inherent instability of falling films generates surface waves and, in some cases, separation vortices, changing heat transfer between the film surface and the wall. The simulations were conducted using the OpenFOAM interFoam solver, with temperature transport equation implemented. Two scenarios were examined: a smooth film case enforced by a free-slip boundary condition at the interface, and wavy film cases generated by imposing disturbances at the inlet. The results reveal that interfacial waves have a dual impact on heat transfer. Wave-induced flow structures enhance mixing near the wall, improving local heat transfer, while thick liquid regions at wave crests reduce thermal efficiency. At Reynolds numbers 10, the smooth film exhibited higher overall heat transfer than the wavy film.