Lower heating value odetermined by subtracting the heat of vaporization of the water v vapor from the higher heating value. OThis treats any H20 formed as a vapor. OThe energy required to vaporize the water therefore is not real ized as heat.Lower heating value determined by subtracting the heat of vaporization of the water vapor from the higher heating value. This treats any H 2O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat