The Solar Uniform Energy Factor (SUEF) Specification for domestic solar water heaters was created in late 2020 by a diverse group of stakeholders from the solar thermal industry. The specification defines the conditions, assumptions, and methodologies to be used to determine a Uniform Energy Factor for domestic water heaters directly utilizing solar energy. It was published as an appendix within the ICC 900/SRCC 300-2020, Solar Water Heating Standard. The U.S. Department of Energy created the Uniform Energy Factor (UEF) metric to quantify the energy efficiency of water heaters in 2014.

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 term is used by the United States Department of Energy to develop and enforce minimum energy conservation standards under the Energy Conservation Program.

The DOE specification that established UEF (10 CFR 430, Subpart B, Appendix E) did not include water heaters utilizing solar energy. Therefore, this specification serves to fill the gap and provides the additional procedures needed to produce a UEF value for solar water heaters. The Solar UEF can then be used alongside UEF values for water heaters using only electricity, natural gas or fuel oil to compare performance on a consistent basis.

ENERGY STAR officially released the finalized 4.0 Specification this past April 2021. The 2020 Solar Uniform Energy Factor Specification is now used in the ENERGY STAR® Program Requirements Product Specification for Residential Water Heaters, Version 4.0 . It replaces an outdated metric called the Solar Energy Factor (SEF) that was used by the ENERGY STAR program in previous specifications.

The major takeaways:

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