Four basic types of natural convection solar air heaters, in many geometries, were tested in a wide range of input solar energy values. Measured values of air flow rate, temperature increase and efficiency are reported. It is expected that the results and conclusions will be valuable in the design of equipment for drying, space heating and other purposes. © 1978.205367369A survey of agricultural dryers (1975) Tech. Rep. T99, , Brace Research Institute, McGill UniversityAung, Fletcher, Sernas, Developing laminar free convection between vertical flat plates with asymetric heating (1972) Int. J. Heat Mass Transfer, 15, pp. 2293-2308Quintiere, Mueller, An analysis of laminar free and forced convection between finite vertical parallel plates (1973) J. Heat Transfer, 95, pp. 53-59Duffie, Beckman, (1974) Solar Energy Thermal Processes, , Wiley, New York