Defkalion and Rossi should should use the methods flow calorimetry described here and in the referenced ANSI documents:
Federal Register, Title 10 of the Code of Federal Regulations (CFR), Part 430—ENERGY CONSERVATION PROGRAM FOR CONSUMER PRODUCTS, Subpart B—Test Procedures Appendix E to Subpart B of Part 430—Uniform Test Method for Measuring the Energy Consumption of Water Heaters http://www.ecfr.gov/cgi-bin/text-idx?SID=c6815929801b9fc181781742d4ac9dfb&node=10:3.0.1.4.18.2.9.6.24&rgn=div9 You do not need to spell out standard industrial techniques. You need to learn them and abide by them, or hire a professional who has been trained to use them. Then you describe what you did, publish a schematic so that people can see that your meters are installed in the correct locations, publish the data, and voila, any person having ordinary skill in the art (PHOSITA) can look up the regulations and confirm that you did it right. Title 10 has schematics showing where the meters should be placed. It describes the tests in detail. Defkalion failed to do a common-sense check of the flow described in this document, which references Title 10: http://www.pensacolaenergy.com/pdfs/Water-Heater-Test1-Protocol.pdf "WATER HEATER TESTING PROCEDURES, OKALOOSA GAS Flow meters and manual balancing (globe) valves will be installed on the outlet piping to ensure all three water heating systems are tested under the same flow conditions. Prior to conducting the tests, the flow meters should be checked for accuracy. This can be accomplished by adjusting the globe valve on outlet piping of each water heater so that the flow meter indicates a volumetric flow rate of 3.0 gallons per minute (GPM). Prior to beginning a test procedure, water flowing from the outlet pipe should be collected in a volumetric basin over a timed interval. The measured volume of water (gallons) should then be divided by the time required to collect the water (minutes) to calculate the flow rate (gallons per minute, or GPM). The calculated flow rate should then be compared to the meter reading to verify accuracy." I, along with many others, repeatedly advised Defkalion to do this. They ignored us. Both Rossi and Defkalion act as they are the first people in history to measure kilowatt scale hot water. They act as if they have to re-invent the wheel. By the way, here are the Federal standards for people making wheels: http://gsi.nist.gov/global/docs/motor_vehicle_parts_guide.pdf
