Overall energy efficiency of an appliance or equipment. Contrast to relative efficiency. Calculated as total energy consumed in active, cycling, and standby modes. Different types of devices have EF computed differently. EF typically displayed very visibly on an item. For example, for a water heater, EF is based on three factors: (1) how efficiently the heating element transfers energy from the outlet to the water, (2) what percentage of energy is lost from cooling of unused, stored hot water, and (3) how much energy cycling between active mode and standby mode uses.