I have to install a electric water tank in my cabin. My well water has approx .09 ppm of iron. Will the iron destroy the water tank much sooner than normal? also if anyone has any suggestions please feel free. What about tankless electric, would that be a better fit with well water.
Unless the iron is ferric red water iron (rust), it is ferrous clear water dissolved iron and it probably will not come out of solution in the water heater, of any type.
The .09 may or may not cause rust stains on surfaces where the water is allowed to evaporate but hardness content is much more critical than iron in that amount; Especially with a tank less heater. All tank less heaters come with a maximum allowable hardness content requirement.
A water softener is used to remove hardness, and iron. If look into a softener, I suggest one with a Clack WS-1 control valve.