The purpose of this paper is to calculate boiler performance by knowing energy losses during steam production. Technical analysis on the boiler is needed, as an effort to increase efficiency and know how much energy is wasted as a loss. Factors causing the greatest heat loss / heat loss in the boiler include: "heat loss due to dry flue gas, steam content in the flue gas, water content in fuel, water content in air supply and others". Heat loss / heat loss or also can be called energy loss is one of the important factors that is very influential in identifying the efficiency of the boiler.For that analysis study is carried out with the calculation of heat loss in order to determine the magnitude of performance decline and the causes of decreased performance. Based on data and analysis of the direct method it is known that the highest energy loss is 26.6% with an efficiency of 74.5%. There needs to be an improvement in the control of the fuel settings and the incoming air optimally by using the Oxygen Trim Control which functions to measure the oxygen concentration in the chimney and automatically regulates the oxygen in the air entering the burner so as to produce combustion with optimal efficiency. And by using an economizer on preheating feed water temperature can increase boiler efficiency