Uncertainty analysis, which is frequently used in conjunction with experimentation, is adapted to the analysis of cross-flow heat exchanger performance predictions (rating, pressure drops, and fluid stream wit temperatures). The basic tools of uncertainty analysis are reviewed, and uncertainty analysis for cross-flow heat exchanger performance predictions is developed and illustrated with a detailed example. The use of uncertainty analysis in cross-flow heat exchanger performance predictions permits error bounds to be placed on predicted performance parameters and gives insight into the fidelity of such predictions. Moreover uncertainty analysis gives considerable insight into the important physical variables and provides a reliable alternative to ad-hoc overspecification of fouling factors. Uncertainty analysis is shown to be a viable paradigm for cross-flow heat exchanger analysis.