What type of boiler uses water as a heat transfer medium?

A water-tube boiler is designed specifically with the intention of using water as the primary medium for heat transfer. In this type of boiler, water circulates in tubes that are heated externally by combustion gases. This design allows for better heat transfer efficiency and higher operation pressures than some other boiler types.

The arrangement of water inside the tubes allows for a direct and efficient exchange of heat between the hot gases and the water, thus raising the temperature and pressure of the water more effectively. This type of boiler benefits from a larger heating surface area and can quickly respond to changes in demand for steam or hot water.

While fire-tube boilers also use water, they do so in a different manner where water surrounds the tubes containing hot gases, which is less efficient at higher pressures. Condensing boilers, on the other hand, are focused more on utilizing the heat from exhaust gases, and electric boilers use electrical energy to heat the water directly. Therefore, the water-tube boiler stands out as the most efficient in terms of heat transfer using water as the medium.