The objective of this paper is to predict compact heat exchanger (CHE) performance for a miniaturized combined heat and power system by a detailed modeling of the complex microchannels and assessing the collector performance using a new reduced order modeling (ROM). The ROM was introduced to decrease the computational size and predict the collector performance with a reasonable accuracy. The CHE is assembled as a stack of counter-flow passages with optimized thickness and an isotropic wire-net (to provide required stiffness and enhance the mixing) which separates the thin partition foils. Computational fluid dynamics (CFD) methodology comprises of conjugate heat transfer (CHT) analysis for a microchannel section and ROM to analyze the entire CHE performance based on the collector performance. The porous medium model, based on the Darcy-Forchheimer law, is modified (constant integration method) to account for the temperature evolution and localized turbulence effects. The resulting microchannel characteristics from a series of three-dimensional CFD-CHT analysis are used to calculate the inertial and viscous coefficients using the constant integration method. These characteristics have been implemented and verified numerically as well as experimentally. The best-revised methodology allows obtaining pressure drop with less than three percent error with respect to the CHT model.