How is boiler capacity determined?

Boiler capacity is primarily determined by the total heating surface. The heating surface area is critical because it directly correlates to the amount of heat that can be transferred from the combustion gases to the water or steam within the boiler. A larger heating surface allows more heat exchange, which can generate steam more efficiently and at a higher capacity.

While fuel consumption, furnace size, and the number of tubes can influence the operational capability of a boiler, they do not directly measure the capacity. Fuel consumption is related to how much energy is provided but does not give a clear picture of heat transfer efficiency. Similarly, the size of the furnace can affect combustion efficiency but does not define how much heat can be effectively transferred. The number of tubes can influence the flow and efficiency but is not a direct measure of the boiler's capacity.

Therefore, focusing on the total heating surface provides the best assessment of a boiler's ability to produce steam or hot water, making it the defining factor for boiler capacity.