Optimization of gas heater Efficiency: Impact of nozzle design and combustion modifications

• Nozzle design optimization increased heater efficiency to 77.78%. • Heat-retaining plate increased efficiency from 68.6% to 73.4%. • Flue and combustion chamber modifications enhanced heat transfer to 76%. • Nozzle and burner tuning minimized CO emissions to 14 ppm. • Structural changes in the furnace optimized gas flow and energy use. Improving the thermal efficiency and emissions performance of domestic gas heaters is essential for reducing residential energy consumption and mitigating urban air pollution. This study presents a structured, experimentally validated framework for optimizing a conventional gas heater through fifteen sequential combustion and heat recovery modifications. Unlike prior studies that focus on isolated design changes, our approach applies a stepwise, system-level strategy that integrates combustion geometry and flue pathway enhancements to improve energy efficiency and pollutant control simultaneously. Key interventions included nozzle diameter reduction (from 270 to 220), installation and perforation of a heat-retaining plate, and the addition of diagonal flow barriers and internal flue grooves to extend the exhaust path and enhance turbulence. Each modification was evaluated for its impact on thermal efficiency and CO emissions. While structural enhancements initially caused CO levels to spike up to 1460 ppm, subsequent tuning—including the use of a 220 optimized nozzle (2.2 mm diameter) paired with a matched burner—successfully stabilized combustion. The final configuration achieved a thermal efficiency of 77.78 %, up from a baseline of 68.6 %, demonstrating a 13.3 % absolute efficiency improvement and a 99 % reduction in CO emissions (1460 to 14 ppm). These results confirm that coordinated, low-cost geometric modifications can overcome performance trade-offs typically seen with single-parameter changes. The proposed framework offers a scalable and practical solution for retrofitting legacy heating systems to comply with modern energy efficiency and air quality standards.