What type of boiler requires firing through a furnace?

The fire-tube boiler is designed such that the combustion gases pass through tubes that are submerged in water. This design necessitates firing through a furnace to generate the needed heat. In a fire-tube boiler, the heat from the combustion process heats the water surrounding the tubes, producing steam or hot water for various applications.

In contrast, a condensing boiler operates by extracting additional heat from combustion gases, which condense and release latent heat. This type does not rely on traditional firing through a furnace but rather utilizes a heat exchanger.

Electric boilers generate heat through electric resistance and do not require a furnace or combustion process at all. They convert electrical energy directly into thermal energy.

Steam boilers can also be fire-tube or water-tube types but do not inherently require firing through a furnace unless they are specifically designed as fire-tube units. Therefore, the unique attribute of the fire-tube boiler, with its reliance on a furnace for heat generation through combustion, solidifies its identity within boiler types.