I feel Phase III makes a great tank but the outer tank is steel, you'd probably be better with an all stainless tank with stainless or copper/nickel coil because of the oxygen in the system. 40 gal.Crown Megastore and Burnham Alliance are all stainless but the coil is only 3/4" piping. Superstore uses 1" boiler piping with cooper/nickel HX piping.