Pre-evacuation creates a closed vacuum environment inside the boiler, which is then filled with heat medium water. Heating generates negative pressure steam; its condensation heat warms cold water in the heat exchange tubes, continuously supplying hot water. The heat medium remains sealed in the vacuum chamber during operation, offering convenient installation, easy maintenance, environmental protection, and energy savings.

The lower part comprises a combustion chamber and heat transfer tubes, while the upper part contains a vacuum steam chamber with a U-tube or straight tube heat exchanger. Operating under negative pressure, the boiler is inherently safe. It can simultaneously provide hot water at multiple temperatures for different applications, reducing overall costs.