http://cwc-das.com/logger//tabs.php?loggerids=485E700680A6C389 I don't get into the green room too much as most of my expertise lies in pipefitting and hydronics. I think however that many of you considering solar hydronic heating may find the link above very interesting. On of the guys from the Wall at www.heatinghelp.com has a monitored side by side comparison of flat panle collectors vs evac tube going on and the results can be viewed live at the link. It contains historical KW harvested as well as tank temps weather conditions etc etc. He's done a really nice job of presenting this data.