Uniform Energy Factor (UEF)

The Department of Energy (DOE) enforces energy conservation standards and testing procedures for various everyday appliances and equipment, including water heaters, refrigerators, air conditioners, clothes dryers, lighting, and more.

The Uniform Energy Factor (UEF) serves as the DOE's latest metric for conveying the energy efficiency of residential water heaters. Previously, efficiency was measured by the Energy Factor (EF). However, in June 2017, the DOE revised the test procedures and metrics to introduce UEF. This regulatory update aimed to facilitate "apples-to-apples" comparisons between two water heaters and altered the way energy efficiency, capacity, and first-hour rating are reported and discussed.

UEF ratings categorize water heaters into four bins based on different levels of hot water usage and evaluate their performance accordingly. A water heater's UEF within its bin is determined based on its first-hour rating. A higher UEF indicates greater energy efficiency and lower operating costs compared to other water heaters in the same bin. It's important to note that a water heater's UEF can only be compared with water heaters within the same bin. For example, a water heater in a high bin with a UEF of 0.95 may not perform identically to one in a low bin with the same UEF of 0.95.

The predetermined hot water usage applied to a water heater based on its bin helps determine its annual operating cost.