The theory of a glazed transpired collector solar air heater in natural convection mode has been developed. This was aimed at generating a framework for the experimental study of the performance of the collector. The theory involved the definition of some of the collector’s main geometries, the formulation of the energy balance on the collector, and the driving forces within the collector. The dimensional analysis was then applied to the formulations to obtain relationships between important dimensionless groups. The theory of the glazed transpired collector in natural convection mode provides a basis for the development of the collector for application in the areas of space heating and crop drying. This type of collector provides a solution to the challenge of space heating and crop drying at locations where electricity is not available and photovoltaic power is not affordable. It could also contribute to energy savings since it requires no electricity to work.