In the present study, the thermal and hydraulic performance of the triple-helical tube heat exchanger were experimentally investigated. The effect of coil radius, inner annulus spacing, water inlet temperature, flow arrangement, as well as Dean number were the main points of this study. Five test specimens with different coil radiuses of 150mm, 125mm, and 90mm and with different inner annulus spacing of 6.2, 9, and 12mm were examined. The test specimens were designed, manufactured and tested to study the influence of key design parameters on triple-helical tube heat exchanger thermal and hydraulic performance. The experimental runs were carried out at Dean number 400 ≤ De_h ≤ 5500 corresponding to Reynolds number 2700 ≤ Re_h ≤ 31000 for the hot water side, and at water inlet temperature 50°C ≤ T_h,i ≤ 80°C. The results revealed that, the triple-helical tube heat exchanger showed a significant enhancement of the Nusselt number compared to double-helical tube heat exchanger by 147.6% and 108.8% for both counter and parallel flow patterns, respectively. Also, with decreasing the water inlet temperature from 80°C to 50°C reflect on increasing Nusselt number by 61.5%, while the increment in pumping power is approximately neglected. Moreover, with decreasing coil radius from 150mm to 90mm and inner annulus spacing from12mm to 6.2mm a significant increase in Nu occurs by 55% and 133.2%, respectively. A general correlation for predicting Nu, f, and ε were presented.