Originally Posted by Jdslep
On the RIS you could mash thicker (1qt/lb) for 5 gal mash water. 2 gallons gets absorbed by grain (0.1 gal/lb). To reach 7 gal pre-boil you spare with 4 gallons. I don't know how you got 20 gallons.
A combination of bad assumptions, bad calculations, and a case of drinking and typing.
I have no idea how I got 20 gallons either. My original assumption was about 24 lbs of grain, 1.25 qt/lb for BOTH mash and sparge, and 0.1 gal/lb absorption rate. That gets me to 14.4 gal pre boil when I recalculate now.
With that said, I've learned a bit more since yesterday, thanks to these replies and a bit more research. Mashing thicker at 1 qt/lb would get me 5.4 gal from the first runnings. I've learned the sparge water does not need to be so thin, so pre-boil volumes quickly become more manageable.
On a side note, I made the plunge and bought all my AG equipment today: 1 deluxe pot, 1 basic pot, mash tun cooler, burner and immersion cooler.