But why would it really matter? As long as it is within the normal range, all would be good.
The wattage that an element draws is dependent on the mains voltage. The mains voltage can and does swing by as much as 10VAC due to demand and/or re-configuring of the power grid. I have measured voltages ranging from 118VAC to 127VAC on my 120VAC outlets. I mentioned earlier that my Blichmann 2250W BoilCoil has a resistance of 7.2 ohms, and that power in watts is equal to voltage squared divided by resistance.
P (watts) = 118 * 118 / 7.2 = 1934W
P (watts) = 127 * 127 / 7.2 = 2240W
The difference in power between the two voltages is 306W. That power difference is significant enough to notice a difference in heating time. A watt is 0.24 calories per second; therefore, 1934W = 464 calories per second and 2240 = 538 calories per second. A calorie is the amount of heat energy needed to raise one gram of water one degree Celsius*
. One gallon of water contains 3,785 millimeters of water. One milliliter of water weighs one gram; therefore, one gallon of water weighs 3,785 grams.
starting_boil_volume = 6.5 gallons/24603ml
mash_runoff_temperature = 151F/66C
boil_temperature = 212F/100C
temperature_delta = 61F/34C
We need to raise 24603 milliliters of wort 34 degrees Celsius.
time_to_raise_boil_1934W = 24603 / 464 * 34 / 60 = 30 minutes
time_to_boil_2240W = 24603 / 538 * 34 / 60 = 26 minutes
Four minutes is a significant difference if one does not have one's kettle alarmed.
* Wort is denser than water.