Question

the heating of water by electric rod/geaser is based on what effect?

Answer 1

Heating through geaser is on thermal effect.

Answer 2

You have thrown in a lot of variables. Let me reduce them before.

Let us assume you have to heat (say) 20Ltrs of water to a temperature of 80 degrees Celsius from 20 degrees(ambient temperature).

Now, to equal to heat transferred from water to atmosphere. Geyser on the other hand, having the advantage of insulation, will still be able to heat water without losing heat to atmosphere, although it will take a very long time and I don’t think you will like to take a bath after waiting for may be 2-3 days in worst case. Still, a point will come when geyser will also stop heating as in spite of the insulation, there will be some losses.