Ash is one of the most studied but poorest understood characteristics. Based on the latest summary on chemical ash composition of varieties of biomass and coal, specific enthalpy, physical, and chemical exergy of biomass and coal ash were calculated then studied statistically. Three correlations were derived for estimating specific enthalpy, physical, and chemical exergy of ash, respectively. Then the ratios of the energy and exergy losses with discharged ash indicate that ash should be taken into account in an accurate exergy analysis of a process that simultaneously involves fuels with high ash content and a high exhaust gas temperature.