During our work on efficiency standards for electric water heaters, we discovered significant discrepancies between the rated and tested efficiencies of the highest rated electric resistance water heaters. For high efficiency electric resistance water heaters with an Energy Factor above .92, the heat losses are so small that minor flaws in the tank or obscure problems in the test procedure become more apparent. This seminar reports on our investigation into the causes of inconsistent results obtained during testing of high efficiency electric resistance water heaters at different test labs. We discovered some reasons for the inconsistencies and have some recommendations for improvements to the test procedure.