Which type of boiler requires the least square footage of heating surface for 1 hp?

The watertube boiler is recognized for requiring the least amount of square footage of heating surface per horsepower. This design facilitates the circulation of water through tubes that are exposed to hot gases. Since the heating surface is primarily within the tubes and directly in contact with the fire, these boilers can generate steam more efficiently compared to other designs.

The compact nature of watertube boilers allows for a greater amount of water to be heated more quickly. This efficiency stems from their construction, where water is forced to circulate through the tubes, enhancing heat transfer and minimizing the required heating surface area. This characteristic not only aids in achieving higher steam generation rates but also leads to a design that is responsive to load changes, making it suitable for a variety of applications.

In contrast, other boiler types such as firetube and horizontal return tubular designs typically require more square footage of heating surface to achieve the same horsepower output because they rely on the heat transfer from combustion gases passing over the water contained in the shell or larger bodies of water. Such designs inherently have limitations in efficiency and space utilization compared to watertube configurations.