EF (Energy Factor)

The Energy Factor (EF) is a measure of a water heater’s efficiency, indicating the amount of hot water produced per unit of energy consumed over a typical day. It takes into account factors such as recovery efficiency (how quickly the heater can warm incoming cold water), standby losses (heat lost from the water heater when not in use), and cycling losses (energy lost during water heating cycles). The EF rating helps consumers compare the energy efficiency of different water heater models, with higher EF ratings indicating more efficient units. EF is being phased out and replaced by the Uniform Energy Factor (UEF) in newer efficiency standards, but it remains a useful metric for understanding water heater performance and energy consumption.