I have two S421 kits that I installed last year but I don't know if I am getting the maximum heat transfer out of them. The S421 kit installation (http://www.smartpool.com/website/manuals/S421.pdf) shows the panels are are connected in series on the feed side and capped on the opposite side. The S425 kit (http://www.smartpool.com/website/manuals/S425.pdf) instasllation diagram shows a different configuration where as the panels are linked together on the far end then feed end. The S425 installation looks like it would absorb more heat as the water is forced through one panel at a time rather than the S421 installation that forces water through the same ends of all collectors. I checked the collector panel part numbers and to see if they are the same buy unfortunately the part number for S421 is not in the manual as is in S425. Can anyone confirm which installation would be better?