i heat with an eko-40 and 500 gallon storage i plan on adding 500 more. it is plumbed hot water to the top of tank also draw off the top for heat when needed cold water return to the turn bottom. i know some use dip tubes and keep the tanks seperate. others connect the tanks with mutiple ports and supply and return the way i have the one tank now .is one way more effiecent than the other.? some advice would be helpful. thanks dave