In this work, the thermo hydraulic performance of a proposed design of an air-to-water double pipe heat exchanger with helical fins on the annulus gas side, is numerically studied. Three-dimensional computational fluid dynamics (CFD) simulations are performed, using the FLUENT software in order to investigate the gas side fluid flow, turbulence, heat transfer, and power consumption for different configurations of the heat exchanger. CFD performance analysis is conducted under turbulent flow conditions for configurations with helical fins. The numerical model is first verified against experimental data available in the literature, for a double-pipe heat exchanger with longitudinal fins. Then, longitudinal fins are considered as a reference configuration and a comparative analysis of the thermo hydraulic performances of the different helical fin configurations and the reference configuration is conducted. The flow field characteristics of the helical fin configurations are clearly demonstrated and discussed. Key design parameters such as the heat transfer coefficient, pressure drop, and thermal performance enhancement factor are evaluated to predict the overall performance of the heat exchangers.