The NANOConVEX working group Cross Impact Matrix addresses the question of how the uncertainty resulting from the characterization of nanofluid properties affects the engineeringly important parameters of heat exchanger design. We study two types of heat exchangers: a double-tube design and a single-tube design, for which experiments with nanofluid have been performed. Moreover, based on the known uncertainty in the properties of nanofluid obtained from the experimental characterization, we use the stochastic collocation method to propagate the uncertainty to the performance of the heat exchanger. Two mathematical models of heat exchangers are considered: a model based on the empirical correlations for heat transfer and pressure drop and a model based on CFD simulations. The results indicate the uncertainty in the heat exchanger figures-of-merit, Nusselt number, pressure drop, friction factor and outlet temperature and the relative importance of uncertainty of nanofluid properties: thermal conductivity, heat capacity, viscosity, and density.