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Originally Posted by pete c
This system would circulate the boiler water only which transfers heat to the potable water via a coil in the tank. pumping the potable water itself up to the roof would likely end up turning the whole thing into a bacteria generator. it would also mean having to seperate it completely from the boiler loop.
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Normally these use some heat-transfer type fluid, but you could do it with what usually goes through the water heater.
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I think maybe many lengths of thin pipe in parrallel would be most efficient.
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The pipes are laid parallel, but connected in a serial way, so the exposure time on the roof is maximized.
Make sure the pump pressure isn't too much for the PVC tubing, and not giving too fast a flow (water flowing too fast through the collector will absorb less heat - it simply won't have time for that.)
If the pipes are some distance apart, enough to let sun through, you could put a mirror underneath them or paint the area below white. It'll reflect some of the heat into the other side of the pipes as well.