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Abstract The thermo-hydraulic and exergy characteristics of a new design called a triple tube helical coil with an inner triangular twisted tube, TTHCITTT, were explored experimentally. The structure of the new design involved a modified inner twisted fluid path for the inner tube of a triple tube helical coil with an inner triangular twisted tube. The study involved the impact of various designing parameters such as twisted pitch ratio, coil torsion, coil inclination angle, Dean number, and double tube helical coil with an inner triangular twisted tube, as a particular reference. The experimental runs were carried out at a wide range of inner annulus Reynolds numbers from 3000 to 26,900 corresponding to velocities of 0.05 to 2.05 m s−1. The main remarks show that the triple tube helical coil with an inner triangular twisted tube presents superior thermo-hydraulic and exergetic characteristics compared to the double tube helical coil with an inner triangular twisted tube by 73.68%. While the twisted pitch ratio increased from ∞ (smooth) to 4.69, the Nusselt number was enhanced by 24.7% at the expense of increasing the friction factor by 36.4%. The coil torsion presents a noticeable impact on increasing the Nusselt number by 18.8% while the increase in f h is approximately 12%. The coil inclination angles of 0° and 90° present a higher Nusselt number compared to that of 45° by 9.3%. The maximum thermal performance factor reached 2.12 for a twisted pitch ratio of 4.69 and coil torsion of 0.068 and at a coil inclination angle of 90°. The smooth tube predicts a higher exergy destruction rate and dimensionless exergy loss than the corrugated tube by 25% and 26.9%, respectively. New correlations to predict the Nusselt number and the friction factor were correlated. Graphical Abstract