Water Heater Energy Use, How calculated?


My electric water heater has a sticker that says it uses 4720 KWH/year. How is that number calculated?
I assume there's a standard somewhere with assumed temperature for input water and air ambient and some number of gallons heated.???
I can calculate the energy needed to heat the water I use. I need a way to estimate the energy radiated from the tank. I'm way to lazy to try to measure it. Thanks, mike
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mike wrote:

EPA/DOE Energy Star tests -- they're not worth much for anything other than relative rankings.
--
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Get used to it. The current "Cap and Tax" energy bill that just left the house will be mandating an energy star rating for your whole home. You won't be able to sell it or get financing without one.
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Search google for 'WHAM, water heater analysis model.'
:http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/D-2.pdf
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These numbers are used for comparison purposes. One easy way to measure usage is to do without hot water for 24 hours and read your elec meter before/after. Or, connect a kw-hour meter to your heater.
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Andy comments:
Maybe the OP was talking about metric pounds, which are about 25% heavier...
Andy in Eureka, Texas ..... where everything is 25% bigger.
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