Excess air adalah udara berlebih yang berfungsi untuk pembakaran di dalam furnace terjadi dengan sempurna. Penelitian ini dilakukan untuk mengetahui pengaruh excess air terhadap efisiensi boiler dengan menggunakan metode heat loss ASME PTC 4-2008. Pengambilan data dilakukan di PLTU 2x16 Mw menggunakan batu bara dengan nilai kalori 4879 kcal/kg. hasil penelitian menunjukkan bahwa nilai efisiensi boiler tertinggi sebesar 84.08% dengan nilai excess air 18.35% yang menghasilkan nilai kerugian panas karena dry flue gas 3.790%, nilai kerugian panas karena moisture di udara 0.147% dan boiler heat credit 0.745%. Nilai excess air sebanding dengan kerugian panas moisture di udara dan kerugian panas karena dry flue gas, akan tetapi berbanding terbalik dengan efisiensi boiler, serta nilai boiler heat credit sebanding dengan efisiensi boiler. Nilai excess air optimum yang dihasilkan adalah 18.35%.

Excess air is more air that serves for combustion in the furnace to occur perfectly. This research was conducted to find out the effect of excess air on boiler efficiency using the ASME PTC 4-2008 heat loss method. Data collection is carried out at the 2x16 Mw power plant using coal with a caloric value of 4879 kcal / kg. The results showed that the highest boiler efficiency value of 84.08% with an excess air value of 18.35% resulting in a heat loss value due to dry flue gas 3,790%, heat loss value due to moisture in the air 0.147% and boiler heat credit 0.745%. Excess water value is proportional to moisture heat loss in air and heat loss due to dry flue gas, but is inversely proportional to boiler efficiency, and boiler heat credit value is proportional to boiler efficiency. The optimum excess air value produced is 18.35%.