Correct me if I'm wrong, but lets say I have 20GAL @ 200F and 20GAL @ 50F, they should both finally equal out @ 125F each correct? The first 20-30F heat transfer should be quite quick, but then drop off and take some time to complete the rest, which I'll confirm with a test.
Yeah, I could either throw ice in the HLT, or instead of recirculating the water out the ball valve and back in the top, I could connect the ball valve to the drain and fresh cold water in through the top....
Anyway, something to try. if it doesn't work that great, then I'll discard the idea...but I got a feeling it will work pretty good. The heat transfer is going to be pretty good through a 50' coil.