The specification used to calculate efficiency must be based on the fuel to be used at the installation. However, if this higher efficiency fuel is not available, the boiler will never operate at the higher efficiency level. Excess air is supplied to the boiler beyond what is required for complete combustion. A certain amount of excess air is provided to the burner as a safety factor for sufficient combustion air. Excess air, however, uses energy.
Heat is absorbed by the air instead of being transferred to output, and efficiency falls.
No efficiency benefit occurs during operation unless a reliable oxygen trim system is provided and the burner is of very high quality. Ambient Air temperature and Relative Humidity Ambient conditions have a dramatic effect on boiler efficiency. Radiation and Convection Losses Boilers are insulated to minimize heat losses from the vessel. However, every unit experiences some losses. These losses are determined by the boiler skin temperature, amount of surface area, and ambient conditions.