At what elevation should the pump and heat exchanger be installed vis a vis the pool water level for best operation on a 27' AG pool? Or does it even make a difference as long as its below the water line? I also see a lot of people around here(eastern Canada) using a long coil of black plastic pipe on the roof tops facing the sun. I don't plan on running the main pool pump during the day so would this coil of piping require its own smaller circ pump?