A Taguchi-based Analysis of Variance (ANOVA) was conducted on a Triple pipe heat exchanger configured as a latent heat thermal energy storing system with stearic acid as a phase change medium (PCM). In this setup, stearic acid occupies the middle annular region, while water, acting as the working fluid (HTF), goes through the inner and outer annular tubes. Key design variables—fin geometry (G1–G4), mass flow rate (ranging from 0.11 to 0.45 kg/s), and working pressure (0.6–0.9 kg/cm²)—were investigated to optimize thermal effectiveness and energy storage capacity. The Taguchi method was employed to perform the optimization, and experimental runs were designed based on the L16 orthogonal array. Statistical analysis was carried out using Minitab software to assess the influence of all factors. Main effect graphs for both effectiveness and energy storage were generated to identify the optimal configuration. The study found that the combination of geometry G4, mass flow rate 0.11 kg/s, and pressure of 0.9 kg/cm² yielded the best performance in terms of effectiveness, whereas the configuration with geometry G1, mass flow rate of 0.11 kg/s, and pressure of 0.6 kg/cm² was optimal for energy storage. A confirmation experiment was conducted to validate the Taguchi optimization results, which showed excellent agreement with experimental data, exhibiting less than 2% error. Furthermore, ANOVA results indicated that fin geometry had the most significant impact on system performance, contributing 97.06% to effectiveness and 45.04% to energy storage, substantially more than the other parameters studied.