What Volume Control said is correct when comparing the series coil with a single coil, if you used the same wire for both. When comparing dual coil series to parallel the voltage of the series will need be quadrupled from that of the parallel if using the same wire. You can also adjust the wire used in order to maintain the same desired resistance regardless of the design. You just have to remember that 2
coils in series will double the resistance of a single coil, while parallel would cut the total resistance to half of the single coil.
As far as performance it is all going to come down to the heat generated by the heating of the
coils. IF you use the same wire for both designs, then at any given voltage the parallel circuit will produce more heat and thus more vape but also increase the risk of underwicking and/or burning depending on the rest of your setup. If however you take this into consideration and adjust the wire used to achieve an identical resistance load in both the series and the parallel circuit then theoretically the performance should be the same or nearly the same. In other words a 2 Ohm total dual coil should perform basically identical regardless if it is series or parallel.
