ABSTRACT THE Hottel-Whillier-Bliss generalized performance equation is probably the best available mathematical description for the performance of a flat plate collector. The most useful form of this equation utilizes the collec-tor heat removal factor and the collector loss coefficient. The collector heat removal factor can be computed from the collector efficiency factor, collector loss coefficient and the flow rate. The purpose of this paper is to present the mathematical formulation for computing collector efficiency and output temperature using derived equa-tions for the collector loss coefficient and the collector ef-ficiency factor. The equations for collector efficiency fac-tor and loss coefficient in this paper provide the basis for analytical prediction of collector performance when used in the Hottel-Whillier-Bliss Equation.