How is boiler efficiency calculated?

Boiler efficiency is fundamentally defined as the ratio of useful energy output to the energy input. This metric provides a clear understanding of how effectively a boiler converts the energy in fuel into usable heat energy. When assessing efficiency, the focus is on the amount of thermal energy that is actually utilized for heating purposes compared to the total energy consumed, which includes losses due to factors such as flue gas losses, incomplete combustion, and heat losses to the surroundings.

While other options may involve activities related to a boiler's operation, they do not accurately define boiler efficiency. Measuring noise levels, for instance, does not provide any direct insight into how well the boiler is performing in terms of energy use. The speed of water circulation might influence the system's performance but does not inherently reflect the energy conversion efficiency. Similarly, analyzing the fuel combustion rate might give some indications about combustion performance, but it does not directly equate to how much of that combustion results in successful heating output. Therefore, the correct method of calculating boiler efficiency is indeed based on the ratio of useful energy output to the energy input.