The influence of economiser tubes on water heating systems is a pivotal factor in enhancing energy efficiency and sustainability. This study delves into the heat recovery mechanisms of economiser tubes, focusing on the thermal performance and optimization of economiser geometry. Through a comprehensive exploration of experimental data and theoretical frameworks, the research highlights the substantial impact of economiser tube geometry on the heat transfer process. It examines various design configurations, operational parameters, and associated environmental implications. Emphasizing heat transfer at multiple locations within the setup reveals the intricacies of economiser design, encompassing factors such as material selection and tube cross-section. Utilizing computational fluid dynamics (CFD), the study’s findings were verified through experimental validation. The economiser tubes feature an outer characteristic length (diameter/width) of 6 mm and a thickness of 1 mm. Transient CFD simulations were conducted to calculate heat transfer from the flue gas to the fluid flowing through the tube (water) using the Ansys (2022 R2) Fluent solver. The study concludes that circular square sections provide more uniform and efficient heat transfer within economiser tubes, and low carbon steel emerges as a suitable material for economiser construction.