I just got my $25 solar pump working and it can only do 1.7GPM. I poured water equal in amount to that which is normally in my kettle after boiling, turned the pump on and it did not come even close to that which I do by hand for 30 minutes during the cool down period.
(Update - I tested it out tonight. By hand, it takes 30 minutes to chill to 72F. With the 1.7GPM pump, it took 37 minutes. I was expecting it to be much worse. Hopefully this does not imply that I am only 7 minutes stronger than a 1.7 GPM pump!)
(Update - I'm definitely doing something wrong. The last 4 batches have taken 45 minutes to cool the wort down to 72F. Perhaps there is a better way to angle the outlet hose which I haven't figured out how to do yet with sanitized rubber bands)
I see that the Chugger has 7 GPM, and know that people use it successfully for wort recirculation.
US Solar has a 3 GPM pump on Amazon for $70.
What is the minimum GPM required for a reasonably efficient pump used for wort recirculation?