I'm halfway through building my 1000 gallon water storage tank. With the cost of copper being what it is, I was wondering if I could use two or three reconditioned thin wall cast iron radiators as heat exchangers for the EKO loop. I know copper has a way higher thermal conductivity than cast iron, about 6-7 times, but I will have a much larger surface area than coil tubes, and my intuition tells me this should work just fine, at a much lower cost. I've seen a couple posts where this is mentioned, but apparently nobody has tried it. Or has someone? Any thoughts from the forum? Thanks.