Originally Posted by tabascom16

It wouldn't matter if you used a brass, steel, cast iron, or whatever material for a fitting (he probably just had a brass unit on hand or is worried the chemicals in the process will eventually eat other materials). The heating element needs to be immersed in the oil no matter what its location is...either in the piping or in the reaction vessel. As long as you are circulating fluid past the heating element you will have a much more energy efficient unit than if the liquid were to stand still.

For example a chunk of ice will melt quicker in 60 degree water that is being circulated versus being immersed in 200 degree water that is just standing still.