What is Uniform Energy Factor and Why Does it Matter?
You may have heard buzz around heat pump water heaters and their record-breaking UEFs, but what does that mean? Uniform Energy Factor, or UEF, is the U.S. Department of Energy’s (DOE) industry standard for measuring water heater efficiency. DOE replaced Energy Factor (EF), the previous measure, in 2017 with the adoption of revised testing procedures and metrics to help consumers and contractors easily and precisely compare the efficiency among water heaters for a given installation scenario. UEF provides a consistent standard, simplifies the selection process, and more accurately measures energy usage under real-world conditions compared to previous measurement models.
A UEF can be considered a ratio that measures how much of the energy a water heater uses is translated directly into heating water rather than wasted by heating the surrounding air or equipment. While the UEF is a vital clue into the efficiency and effectiveness of a water heater, several factors influence how different water heaters measure up in comparison.
How is UEF measured?
To measure UEF, water heaters are separated into categories, or “bins,” representing different daily hot water usage levels. There are four bins – water heaters for very small, low, medium, and high usage. Water heaters are comparable to others within their bin for purposes of rating overall efficiency. A high UEF rating means a water heater is more efficient than others in its bin. UEF is only compared across water heater models that belong to the same bin.
Water heater models are evaluated in a lab that performs a Simulated Use Test, examining water heater efficiency under certain conditions. This test will first determine the water heater’s First-Hour Delivery (FHD) (the amount of hot water a water heater can provide in the first hour of operation).
For the remainder of the test, the water heater’s usage pattern is simulated over 24 hours with specific water temperature, air temperature, and use timing. The results of these tests are combined to determine the overall UEF of the product. The AHRI Directory shows final results for reference by professionals in the industry. ENERGY STAR’s Product Finder identifies UEF for each qualifying unit and allows users to sort water heaters quickly according to UEF.
Overall, UEF more accurately measures energy usage under real-world conditions than previous measurement approaches.
How Does a igher or Lower UEF Affect Me as a Consumer?
As you consider purchasing a new water heater, remember that the higher the UEF, the more efficient the product. It will save you more energy than other products with similar capabilities and result in lower operating costs.
Most traditional water heaters have a UEF of between 0.63 and 0.95. For example, a tankless gas water heater or a standard electric storage water heater might have a UEF of 0.93, representing approximately 93 percent efficiency or just 7 percent of wasted energy involved in the water heating and delivery process.
On the other hand, ENERGY STAR certified heat pump water heaters typically have UEF ratings in the range of 3.3 to 4.1, demonstrating an astounding 330 to 410% efficiency. How is this possible? Heat pumps capture heat from the surrounding air and move it into the water in the tank, similar to a refrigerator or air conditioner. Because heat pumps move heat instead of creating it, they can heat water with 3 to 4 kWh for every 1 kWh used.
Look for the ENERGY STAR label to be sure you are getting an energy-efficient product that has been independently certified to save energy and lower your operating costs for years to come.
What are other measures of water heater performance?
Several different characteristics of water heaters influence overall performance. They may also play into consumer decisions when choosing a water heater. The First Hour Rating / First Hour Delivery (FHR/FHD) is the amount of hot water a water heater can provide in the first hour of operation. For example, a smaller water tank of 40 gallons with a very high-powered heating element might produce 80 gallons during the first hour of operation. In contrast, a lower-powered heating system might require an 80-gallon tank to make the same 80 gallons of hot water in the first hour. Delivery after the first hour is usually reduced until the water heater can heat the water refilled into the tank.
Another important consideration for a water heater is the tank size, which designates the amount of hot water that is always on hold. Tank size also generally translates to how much space the water heater will occupy.
Where can I learn more about ENERGY STAR certified heat pump water heaters?
To learn more about available products and their UEF ratings, visit the product finder pages for ENERGY STAR certified water heaters.
Also, check out resources such as the ENERGY STAR’s Rebate Finder to learn about utility rebates, special offers, and new federal income tax credits of up to $2,000 for heat pump water heaters as part of the Inflation Reduction Act.