he present study attempts to use the methanol–silver nanofluid filled heat pipe heat exchanger and compares the effectiveness as well as the energy saving with pure methanol. A heat pipe heat exchanger has been tested in a test rig under steady-state conditions. The lengths of both the evaporator and the condenser sections of the heat exchanger were 700 mm, and its central adiabatic section had a length of 160 mm. The heat exchanger had 36 plate finned copper thermosyphons arranged in three rows. The inlet air temperature across the evaporator section was varied in the range of 33–43 °C while the inlet air temperature to the condenser section was nearly constant to be 13 °C. First, pure methanol was used as the working fluid with a fill ratio of 50 % of the evaporator section length, and then dilute dispersion of silver nanoparticles in methanol was employed as the working fluid. The nanofluid used in the present study is 20 nm diameter silver nanoparticles. The experiments were performed to compare the heat pipe heat exchanger effectiveness and energy saving, using nanofluid and pure methanol. The inlet air relative humidity across the evaporator section was varied between 35 and 80 %. The sensible effectiveness of the heat pipe heat exchanger obtained from experiments varied about 5–22 % for pure methanol and 9–32 % for methanol–silver nanofluid. Based on these experimental results, using methanol–silver nanofluid leads to energy saving around 8.8–31.5 % for cooling and 18–100 % for reheating the supply air stream in an air conditioning system.