How does scale formation affect boiler efficiency?

Scale formation has a significant impact on boiler efficiency, primarily because it acts as an insulator. When scale builds up on the heat transfer surfaces of a boiler, it creates a barrier between the hot combustion gases and the water or steam inside the boiler. This insulating layer prevents effective heat transfer, meaning that more fuel is needed to produce the same amount of steam or hot water. As a result, the boiler must work harder, consuming more energy and ultimately reducing overall efficiency.

In contrast, while other options suggest potential effects of scale formation, they do not accurately reflect its impact on boiler performance. Scale does not increase the temperature of steam, as that relates more to pressure and heating efficiency. It also does not decrease the need for water; in fact, it can lead to more frequent blowdowns to control concentrations of impurities, potentially increasing water usage. Lastly, scale formation does not improve safety features; in fact, it can lead to dangerous situations such as overheating and pressurization issues, as the insulating effect can lead to localized hotspots and system failures. Thus, the primary concern with scale is its insulating effect, which detracts from the overall efficiency of the boiler system.