There is empirical evidence that instantaneous water heaters do not perform at their rated efficiency when compared to realistic hot water draw profiles. The U.S. Department of Energy’s (DOE) procedure for establishing the Energy Factor prescribes six equal, hourly draws totaling 64.3 gallons during the first 5 hours of a 24-hour testing period. Occupants more commonly make dozens of smaller draws throughout a day. Instantaneous water heaters are subject to significant thermal loss directly following a draw. The DOE procedure does not adequately capture the totality of thermal loses stemming from typical residential use. Based on results of lab and field testing conducted by the Davis Energy Group, the California Energy Commission adopted into California’s Building Energy Efficiency Standards the requirement that the code-compliance software apply an adjustment factor of 0.92 to the Energy Factor for gas, oil and electric instantaneous water heaters. The RESNET Technical Committee proposed amending RESNET’s technical standards to apply the California adjustment factor of 0.92 to the Energy Factor for gas, oil and electric instantaneous water heaters. After an ANSI compliant public review and comment process the RESNET Board of Directors adopted the amendment. The amendment will go into effect on July 5, 2012. To view the adopted amendment click on RESNET Instantaneous Water Heater Efficiency Adjustment
