Nanofluids have often been utilized lately for enhancing the thermal performance of heat transfer devices operating with a working fluid. In this study, using iron aluminate spinel nanoparticles, deionized water-based nanofluids at various mass concentrations (0.5%, 1.0%, and 2.0%) of nanoparticles were prepared and tested as the test fluid inside the heat pipes of the air-to-air heat exchanger operating between hot and cold air passages. The efficiency, as well as thermal resistance of the heat pipes, were investigated under varying Reynolds number combinations of hot and cold air passages. An increase up to 87.2% in efficiency and a decrease up to 71.6% in thermal resistance of the heat pipes were obtained with the utilization of magnetic nanofluid. Furthermore, the effect of nanoparticle concentration on performance was discussed.