T The steam boiler is a very important unit to support the production process in the ink industry. The diesel-fueled water pipe boiler type is used to heat the reactor with a heat level that is adjusted to the needs of the production process. The performance of the steam boiler is thought to have a much lower level of energy efficiency compared to the initial conditions. The basis for analyzing the performance of this steam boiler uses two methods based on the American Society of Mechanical Engineers (ASME) Power Test Code 4.1 (PTC-4.1 Power Test code for Steam Generating Unit), namely the input-output method and the heat-loss method. With the input-output method, the efficiency of the boiler is 82.68% and by using the heat-loss method it is 76.75%. The efficiency of the steam boiler is 76.75% decreased when compared to the initial conditions of the installation. The results of the analysis to increase the value of the efficiency of the boiler by increasing the temperature of the feed water, it is found that the consumption of diesel fuel becomes efficient. And by reducing excess air, the efficiency of the steam boiler increased by 3.04% to 79.79%. Preventive improvements in improving boiler performance will be obtained both in feed water and in the process itself.