heater element?

[dragnracing]

what is the best element size to use for my reflux still. it has a 3.5 gallon boiler. i am certainly not an electrition and know nothing of rheostats and triacs.i was wondering what the simplest way to controle the power? Or could i just use one 1500w and one 1000w element and just unplug the bigger one once at a boil.any help is appreciated