When selecting a buffer tank for use with two tank desuperheater set up, I have seen reference to 50 gallon electric tank (with no power connected I assume). I have also seen plain insulated storage tanks designed for use with hot water circulators (no elements). Surprisingly, the cost on the "storage tanks" seems to be considerably more than comaprably sized electric water heater tanks. Any thoughts on this? I assume the storage tanks are better insulated? Any other differences that effect use as a buffer tank?