I recently received an Ask E Source question about the uniform energy factor (UEF) of different water heaters, and I was confused. After all, we’ve been measuring residential water heater efficiency with the energy factor (EF) metric for more than 30 years. I did some digging and learned that in June 2017, the US Department of Energy (DOE) specified that all residential (and some small commercial) water heaters will be evaluated through UEF instead. I was surprised I hadn’t heard about this change, and I immediately did what any self-respecting energy technology nerd would: I dove headfirst into the DOE’s Appendix E to Subpart B of Part 430: Uniform Test Method for Measuring the Energy Consumption of Water Heaters to learn more.

Did you know the standard water heater efficiency metric quietly changed from EF to UEF in June? Tweet this!

I wasn’t the only one who missed the memo on this federally mandated change in efficiency metrics. After searching through E Source tools (such as DSMdat and Measure Insights) and a handful of other sources, I discovered that all utility efficiency programs in North America are still qualifying water heaters based on EF, even as products reporting EF disappear from the market. That’s a problem. If utilities don’t change their program criteria and supporting assumptions soon, it could lead to customer confusion and reduced program participation rates.

I wasn’t the only one who missed the memo on this federally mandated change in efficiency metrics.

The good news is Energy Star adjusted its Water Heater Key Product Criteria. Products can be Energy Star–certified if they meet EF or UEF criteria, but Energy Star warns not to compare the two values. These criteria could provide a framework to help utilities adapt their program assumptions and specifications. Because this metric change has already gone into effect, utilities need to work quickly if they want to make sure their customers don’t end up in hot water.

Want more information? Members of the E Source Technology Assessment Service can check out my report Water Heater Efficiency Metrics Are Changing—Are Your Program Assumptions?—it provides more details on how EF and UEF differ and how utilities should move forward with this new metric.

Contributing Authors

Senior Manager, Technology Assessment

Essie Snell researches, writes, and presents on a wide range of established and cutting-edge energy-efficiency technologies spanning multiple sectors...