Class 5 Boiler Practice Exam 2026 - Free Boiler Certification Practice Questions and Study Guide

Fouling refers to the accumulation of unwanted materials on the heat transfer surfaces of the boiler, such as scale, sludge, or other deposits. This buildup can significantly impede the efficiency of heat transfer within the boiler system. When heat transfer surfaces are fouled, the heat exchange becomes less effective, causing the boiler to work harder to produce the same amount of steam or hot water.

As a result, the energy consumption increases while the actual output may decrease, leading to a lower overall efficiency. This decrease in boiler efficiency means that more fuel is needed to maintain the desired output, which can also increase operating costs and contribute to wear and tear on the boiler components. Therefore, the potential consequence of fouling is a decreased boiler efficiency, which is the correct answer.