Well, I just tested the flow rate through my chiller and it works out to 40 GPH. I think I'll return it and get one that is rated higher (wow, 1/6th the "rated" flow rate, I wonder how they actually test them to get 264 GPH). The next one up is 620 GPH for $35. Assuming I get 1/6th of that I should be at 100 GPH. I can't find the web site where I saw a test of immersion chillers and recirculation of ice baths, but I seem to remember 100 GPH was the sweet spot.