This paper deals with the improvement of thermal performance of the heat recovery system in air-to-air unit by using a nanofluid of TiO2 particles and distilled water. The experimental set-up equipped with 15 copper pipes of a 1000 mm length, 10.5 mm inner diameter; and 12 mm outer diameter was used. The evaporator section consists of 450 mm of heat pipes, the condenser section is 400 mm, and the adiabatic section is 150 mm. In experimental studies, 33% of the evaporator volumes of heat pipes were filled with working fluids. Experiments were carried out at temperatures between 25 degrees C and 90 degrees C by usingfive different cooling air-flows (40, 42, 45, 61, and 84 g/s), and two different heating powers (3 kW and 6 kW) for the evaporation section, to determine heat removed from the condensation section. Trials were performed for distilled water and nanofluid respectively, and the results were compared with each other. Results revealed that a 50% recovery in the thermal performance of the heat pipe heat recovery system was achieved in the design using TiO2 nanofluid as the working liquid, at a heating power of 3 kW, air velocity of 2.03 m/s and air-flow of 84 g/s.