A steam boiler with manual feeding into the furnace offers versatility, allowing fuel of varying sizes and shapes to be burned efficiently. Its minimal radiation losses, due to the furnace being internal and surrounded by water, enhance energy efficiency. The three-pass construction ensures quick steam generation, reducing the time required from cold start to working pressure. Ideal for process industries that demand continuous, uninterrupted steam, the boiler has a compact design with minimal space requirements. It is easily erected and commissioned, and is less susceptible to poor water quality, ensuring reliability with low power consumption and minimal need for highly skilled operators.