If iuse brewsmith it tells me typically to
Mash X gal at Y degrees to achieve 150 mash for Z min
Mash out X1 gal at Y1 (200 deg) for Z1 (2) MIN
Sparge with X2 gal at Y2 degree. I fly sparge that.
So if I heat water to 200 for mash out and use 2 gal, I have X2 gal left in HLT and only have a few minutes to get it down to 168 (Y2) to fly sparge. I was going to add ice to drop this temp and wondered if there was a calculation readily available. My fizix books are long gone