Personally, I pick whatever measuring system makes the calculation easier. I'll let you look up the conversions, but we could call 16 oz half a liter, and 100 degrees f is 55 degrees C. So, without having to use a calculator, you can say that 500 grams of water would require 27500 calories to add 55 degrees. That's about 32 watt-hours, or roughly 1900 watt minutes.
Electric heating elements are considered 100 percent efficient -- in other words, there is no "waste" heat. However, if you we are using an immersion heater in a pan of water, you'd have heat losses to the environment. In a well-insulated system, such as a water heater, the actual efficiency can be over 90% (and this depends strongly on how efficiency is measured: If you input the heat, turn off the power, and then come back in a week to check the temp rise, you will find the tank cold).
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Heating Load
Re: Heating Load
