Class 5 Boiler Practice Exam 2025 - Free Boiler Certification Practice Questions and Study Guide

The primary fuel used in a fire-tube boiler includes natural gas, oil, or coal, which serve as the main energy sources to heat the water within the boiler. In a fire-tube boiler, combustion takes place within tubes that are surrounded by water. As the fuel burns, hot gases travel through the tubes, and the heat generated transfers to the water, causing it to steam.

Natural gas is a common choice due to its high efficiency and cleaner combustion compared to other fossil fuels. Oil is another effective fuel option, particularly in areas where gas is not readily available. Coal is also used in some applications, especially in larger industrial boilers, as it remains an abundant resource.

Electricity, biomass, and solar energy, while viable fuel options in different types of boilers and systems, are not typical primary fuels for fire-tube boilers. Electricity may be used in electric boilers, biomass is often used in special biomass boilers, and solar energy requires a different setup entirely, such as solar thermal systems. Hence, natural gas, oil, and coal make up the primary fuel sources for fire-tube boilers due to their reliability, availability, and suitability for the combustion process within this type of system.