In Reply to: Re: water tank heater watage posted by Larryb on December 31, 2017 at 22:48:21:
According to the wire tables, 14 Ga. Copper has a resistance of 2.58 ohms per 1000 ft.
Two,100 ft.14 gauge copper conductors would be .516 ohms. At the 12.5 amp draw of your heater that would result in a voltage loss of approximately 6.45 volts or 5.38%.
For your distance 14 gauge would be fine.
For the permanent wiring I also would use 12 gauge.