I built a few of these and they work just fine. Because I am a little cheap so I look for ways of doing things that don't need much money . I started with some plastic CPVC pipe taking the tubes and cutting them into many vertical tubes connected top and bottom with other tubes painted them black but before assembly I took used clear water bottles small and put over the tubes. Here is a short video using the same idea. I took an old water tank and connected the bottom connection and the input water also the bottom of the plastic pipe. There was a connection in the middle of the tank which I put the out flow of the pipes [top] and the top connection of the tank was the out put [hot water]. My system puts out water at about 140 - 150 degrees free hot water.