How is the heating surface of a water tube calculated?

The correct formula for calculating the heating surface of a water tube is represented by the equation that involves the product of π, the diameter, the length, and the number of tubes (HS = Pi x D x L x N). This approach makes sense because the heating surface area of a water tube is determined by the surface that is exposed to the hot gases or fluids, which is critical for efficient heat transfer.

In this equation, π (Pi) takes into account the circular cross-section of the tube, D represents the diameter, L is the length of the tube, and N denotes the number of tubes. The heating surface area is essential for understanding how much heat can be transferred, which in turn affects the efficiency and output of the heating system.

The other options either do not include the necessary components or misrepresent the relationship needed to compute the heating surface effectively. Therefore, option A is the most accurate and relevant choice for determining the heating surface of a water tube boiler system.