The fuel specified has a dramatic effect on efficiency. With gaseous fuels, the higher the hydrogen content, the more water vapor is formed during combustion. The result is energy loss as the vapor absorbs energy in the boiler and lowers the efficiency of the equipment. 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.