Under the RESNET® Standards, “For commercial water heaters where EF or UEF is not available, an Approved commercial hot water system calculator shall be used to determine the EF or UEF.” The RESNET calculator previously approved for use, determined EF from other values, such as thermal efficiency and standby loss. This RESNET calculator is now being replaced with an updated version, that can directly determine UEF. The new UEF Calculator for Commercial Water Heaters (August 2026) is now approved and available for use. Please share it with your rating staff and use it in place of the earlier version. Where an EF is still needed, enter the calculated UEF into this existing RESNET calculator to convert UEF to EF: https://www.resnet.us/wp-content/uploads/RESNET-EF-Calculator-2017.xlsx Raters should use the updated tool whenever a commercial tank water heater in a residential application does not have a published EF or UEF value. The previous Commercial Hot Water calculator should no longer be used. For ratings that are currently in process but not yet uploaded, Raters may choose to update to the new calculator, which typically produces a higher EF than the previous tool. Using the calculator: Locate the specific water heater model in the AHRI Directory (ahridirectory.org). Enter the applicable values — Measured Volume, Thermal Efficiency, and either the combustion or electric-resistance Input Rate and Standby Loss — in the yellow input cells. For electric resistance storage water heaters without a listed Thermal Efficiency, enter 98. Enter the resulting UEF and First Hour Rating (FHR) into your energy rating software. Where the rating software requires EF to be entered, use this RESNET calculator to convert UEF to EF: https://www.resnet.us/wp-content/uploads/RESNET-EF-Calculator-2017.xlsx The updated file is also available on the RESNET Website. Please replace any prior copies with this version to ensure ratings are calculated using the current methodology. If you have any questions about the calculator or its use, please reach out to info@resnet.us
