Really nice Water pre-heater. I am planning to make one very similar to yours, except i was thinking of using cheap ABS (black) plastic pipe since copper is SO expensive. I just hate the idea of 9000 watts (grid)heating up 45 degree water from the underground each time we each take a shower. My plan is to use a small water pump to recirculate the cool/warm water from the hot water tank back out to the panel outside, controlled w/ thermostate like yours. The sun is always shining where i live. Looks like your getting great savings already. -Good work!