Structure:
It is the same as the regular one, composed of the firebox and heat transfer tubes. The upper parts is equipped with a heat exchanger. There is also an expansion tank at the top. Generally, the boiler works under normal pressure. So it's absolutely safe. The thermal media in the boiler isn't in or out when the boiler is working. It transfers the heat between heat transfter tube and heat exchanger. After being heated, the thermal media will oxygenate and intenerate, and there is no furring and oxygen corrosion. The machin can be used as long as 20 years.

Fuels: Oil, gas or coal, electricity also can be used.
Compact structure, easy to mount and low engineering cost.