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withered_preacher
Energy used heating or boiling water in a kettle. Assuming no losses. There actually isn't really anywhere for the energy to go in a kettle other than into the water, it's quite efficient.
Specific heat capacity of water: 4200 J/kg/K
Lets's say tap water comes out at 15°C. 1 litre water in kettle = 1kg water.
Heat to 92°C = 323.4 kJ = 0.0898 kWh = 1.52p @16.9p / kWh
Heat to 100°C = 357 kJ = 0.0992 kWh = 1.68p @16.9p / kWh
Really not much in it. More of your waste is in the water you heat up and don't use.
I don't know how much you boil off in the few seconds before it shuts off when it's boiling, but it's not going to be much. Latent heat of evaporation of water: 2250 kJ/kg if you want to weigh it. Or 3 kW kettle for however many seconds (best guess).