This document discusses boiler efficiency, including the factors that affect it. It is summarized as follows: 1. Boiler efficiency is determined by combustion efficiency and thermal efficiency. Combustion efficiency depends on unburned fuel and excess oxygen in exhaust, while thermal efficiency depends on heat transfer across the boiler tubes. 2. Other losses like radiation, convection, and blowdown also impact overall boiler efficiency. Efficiency is calculated directly from energy input and output, or indirectly using other parameters. 3. Tips to improve efficiency include preheating combustion air, optimizing excess air, cleaning heat exchangers, and establishing an ongoing maintenance program.