The purpose of a power boiler is to create steam by applying heat energy to water. The necessary heat energy is produced by combustion. Fuel and oxygen are required for combustion to occur. To ensure complete combustion of the fuel in the boiler furnace, enough air must be thoroughly mixed with the fuel. Each power boiler fuel requires a different amount of air for complete combustion and the combustion controls must be designed to provide it. This module describes the role of combustion in power boilers as well as major components and flows of power boiler air systems.