This is a Solar hot water Batch Type pre-heater that pre-heats the water for my hot water tank inside the house. Cost $45.00 to build. I made it out of garage sale and Goodwill items and scrap wood I had laying around. It has been heating water up to 140 degrees and circulates thru the tank by natural flow no pump needed as it is lower than the main tank.
This is what it looked like when I finished. I added extra insulation and foamed all the cracks.