I finally got some of my old 1" copper runs replaced with pex-al-pex, so now I have the raw material to build the heat exchangers I've been planning. I put one of the header units together tonight. After getting all the initial measuring and figuring and prep work done, the actual assembly went pretty fast. There will be 8 in total, out of which I plan to make two heat exchangers for my storage tank--one for heat storage and one for recovery. This project is the result of my being too cheap to buy soft copper coil. So in total, my tank will have 200 feet of Type M 1/2-inch copper and another 80 feet of 1" Type M copper to get the heat in and out. The plan is to connect four units with a 1" manifold arrangement so that they can be positioned vertically in the tank. The heat storage hx will sit on the bottom and extend up about 3/4 of the height of the tank. The heat recovery hx, on the other hand, will hang from the top of the tank to 3/4 of the way down. They will be nested together. Basically, the top hx will be attached to the bottom one in the right position, so the whole thing sits on the tank floor and extends to near the top. That's the plan, anyway. Any reason to think it won't work?