How many square feet of heating surface are required to produce 1 hp in a vertical firetube boiler?

In a vertical firetube boiler, the standard requirement is that approximately 14 square feet of heating surface is needed to produce 1 horsepower (hp). This standard is based on the typical design and efficiency considerations of firetube boilers, where the heating surface area directly correlates with the amount of steam generated and, consequently, the power output.

Understanding the relationship between heating surface area and horsepower helps in determining the required capacity for specific applications in boiler operations. Essentially, the larger the heating surface area, the more steam the boiler can produce, thereby increasing its ability to generate power.

Other options provide alternative figures that do not align with the standard requirements for vertical firetube boilers. Therefore, the choice of 14 square feet reflects the industry-recognized measure necessary for efficient operation at the given horsepower output.