So, this is the actual tank I was thinking of using with my solar panels. It is a 200gal tank with one end cut off standing on its side. You can see in the othe photo the output heat exchanger coil. It consists of 2 runs of 50ft of 3/8 inch pipe. The system is not working now. I'm planning on putting up the 4 to 6 panels in the spring. I do like the idea of building a wooden tank with the insulation inside. This oil tank is more difficult to insulate. I supose wood will not rot or rust if built right. Thanks for all that info Gary from "builditsolar".