Journal of Fundamentals of Renewable Energy and Applications
Open Access

Energy Factor

An energy factor is a metric used in the United States to compare the energy conversion efficiency of residential appliances and equipment. The energy factor is currently used for rating the efficiency of water heaters, dishwashers, clothes washers, and clothes dryers. The energy factor (EF) indicates a water heater's overall energy efficiency based on the amount of hot water produced per unit of fuel consumed over a typical day. This includes the following: Recovery efficiency – how efficiently the heat from the energy source is transferred to the water. The higher the energy factor, the better. Gas water heaters have energy factors between 0.5 to around 0.7. Electric models range from 0.75 to 0.95. ... However, higher energy factor values don't always mean lower annual operating costs, especially when you compare fuel sources. Uniform Energy Factor (UEF) is a new metric for determining the energy efficiency of a water heater. UEF's are determined by the estimated usage of a water heater: When selecting the most efficient unit for you, consider the fuel type and the capacity needs for your home. The higher the energy factor, the better. Gas water heaters have energy factors between 0.5 to around 0.7. Electric models range from 0.75 to 0.95. By varying the tank insulation, burner design, and a few other features, manufacturers continue to make residential heaters more energy efficient.