my question is, if the tanks are the same dia. and the same length and have an equal amount of insulation (with-in-guestamation). Does it make a difference which way they are orientated (in vertical, or in horizontal)? For instance you take two 250 gallon or two 500 gallon propane tanks, plumb them to except hot water up high and draw cold water from down low, does either way have a benefit over the other? With my limited knowledge, I can only guess that having the most or largest dia. connections between the two tanks (equalization), will make the biggest difference. thanks for any suggestions.