This experimental study presents heat transfer and fluid flow characteristics of metallic water nanofluids in an agitated serpentine heat exchanger. Tests are performed using 0.1% wt. concentration of the Cu-water, Fe-water, and Ag-water nanofluids. The effects of flow rate (4-10l/min) and agitator speed (400, 800, and 1300 rpm) are investigated for three serpentine tubes having diameter of 0.9525 x 10(-2), 1.27 x 10(-2), and 1.5875 x 10(-2) m(2) with the same length of 1.6 m. The results show that higher flow rates and agitated speeds result in more heat transfer enhancement. Also, the thermal performance of agitated serpentine heat exchanger improves by using nanofluids at constant operating conditions. However, little pressure drop increment is observed compared to the base fluid. It is also found that the heat transfer enhancement of Cu-water nanofluid, as working fluid, is more intensive than Fe-water and Ag-water nanofluids. Overall, 4.2% and 7.8% improvements in the thermal-hydraulic performance of agitated serpentine heat exchanger might be achieved by using Cu-water nanofluid compared to Fe-water and Ag-water nanofluids. (c) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.