A New DOE Standard for Rating Water Heaters
Water heaters are currently rated by Energy Factor (EF). The EF is determined from a simulated use test that measures the heat out as well as the energy input over a 24 hour period. The EF is the ratio of energy out divided by energy input. The test imposes six large hot water draws on the water heater at one hour intervals at the beginning of the 24 hour period. The total hot water load is 64.2 gallons per day. This test and rating procedure was developed by the US Department of Energy to rate the efficiency of residential water heating products.
The current procedure had several shortcomings:
The New Test Procedure for Residential Water Heaters
New Test Procedure
After several years of rule making, DOE has refined the test and rating procedure to address many of these shortcomings. The new procedure, published in July 2014, determines a new descriptor know as the Uniform Energy Factor (UEF). The new procedure will take effect July 2015. The most important changes include:
- Using a series of more realistic draw profiles with daily water usage that is consistent with the water heater size (i.e., its first hour rating). Three new, more realistic profiles corresponding to low, medium and high water use with 11-12 draw events that total 38, 55, and 84 gallons per day, respectively.
- The range of covered products has been expanded to uniformly consider high efficiency condensing tanks (with high capacity burners) as well as tankless and hybrid products with small amounts of hot water storage.
- Lowering the required supply temperature from 135 degrees F to 125 degrees F to reflect actual settings in homes.