The Department of Energy (DOE) implements energy conservation standards and test procedures for many appliances and equipment that we use every day, like water heaters, refrigerators, air conditioners, clothes dryers, lighting, and more.

The Uniform Energy Factor (UEF) is the DOE’s latest metric for communicating the energy efficiency of residential water heaters. Previously, you may have seen efficiency measured by Energy Factor (EF); however, in June 2017, the DOE changed the test procedures and metric used to communicate the energy efficiency of residential water heaters and created UEF. The new regulation aimed to make it easier to make “apples to apples" comparisons between two water heaters and changed the way we report and talk about energy efficiency, capacity and first hour rating.

UEF ratings are determined by assigning water heaters into one of four different categories of hot water usage and then evaluating their performance based on that usage. These categories are called bins. A water heater is assigned a UEF within its bin based upon its first hour rating. A higher UEF means a water heater is more energy efficient and will cost less to operate compared to other water heaters in the same bin. A water heater’s UEF can only be compared with water heaters within the same bin. For example a high bin water heater with a UEF of 0.95 does not perform exactly the same as that of a low bin water heater with a UEF of 0.95.

Based on the bin in which a water heater is categorized, a predetermined amount of hot water usage is applied to that water heater to determine the annual cost of operation.