This lecture is on natural convection. It addresses the differences between forced, natural and mixed convection. Natural convection over different types of surfaces are addressed and two examples were done, taking into consideration radiation heat transfer. The lecture was presented on 26 April 2018. This lecture is Lecture 15 (2018) of approximately 3 lectures that was based on the textbook of Cengel and Ghajar (5th edition) and was presented as part of a heat transfer class to the fourth-year students by Prof Josua Meyer, Head of the Department of Mechanical and Aeronautical Engineering of the University of Pretoria, South Africa.