I think Heliocol is a really nice system (they used it on the 1996 Atlanta Games' pool roof to heat the Olympic pool) the only drawback is that they don't sell systems for owner builder, they only sell fully installed systems and their price is pretty steep. I'm kind of a handy guy so I'd rather isntall one myself, but if I were to pay someone I'd look at the Heliocol for sure.