<p>The very high temperature gas-cooled reactor (VHTR) enables efficient high-temperature process heat applications, such as hydrogen production. The tube bank intermediate heat exchanger (tbIHX) is a critical component in VHTR-coupled hydrogen production, and improving heat transfer is necessary to ensure efficient production. In this study, the thermal–hydraulic performance of tbIHX with longitudinal triangular fins is numerically investigated. Numerical simulations are conducted to analyse the effect of fin thickness (<i>t</i>/<i>D</i> = 0.08, 0.16, and 0.24) and fin length (<i>L</i>/<i>D</i> = 0.5, 1.0, and 1.5) on flow and thermal performance. The numerical simulations are conducted for Reynolds numbers ranging from 5000 to 25,000, with helium as the working fluid. The results indicate that adding triangular fins significantly enhances heat transfer performance compared to bare tubes. The highest average Nusselt number is observed at Re = 25,000 with the largest fin configuration (<i>t</i>/<i>D</i> = 0.24, <i>L</i>/<i>D</i> = 1.5), leading to a 57.3% improvement. The maximum performance evaluation criterion (PEC) of 1.71 at Re = 25,000 (<i>t</i>/<i>D</i> = 0.24, <i>L</i>/<i>D</i> = 1.5) indicates that the heat transfer surface area can be reduced by 71% while maintaining constant pumping power.</p>