Originally Posted by WaltG
My only options are a 9 qt or 32 qt pot. Tested the boil off rate on my 32qt at about 0.8 gal/hr so biab calc is saying 3.1 gal with just over 2 1/2lb of grain.
With all due respect, I think you are being led astray by Beersmith or another "calculator", and are making this much much more difficult than need be...It's not that hard at all as you will realize after you have done it.
With 3.1 gallons total water, you will lose about .25 gallons to grain absorption, and .8 gallons to evaporation leaving you with about 2 gallons of wort, for a 1 gallon batch
Perhaps you have losses entered into the calculator...IDK, but I don't believe the numbers!
As said above, I would simply mash in your 9 qt pot with 7.5 quarts resulting in 2.07 gallons of mash (8 quarts), you will lose approx .25 gal (1 quart) to grain absorption leaving you with 6.5 quarts preboil, I would sparge a quart through the bag giving you 7.5 quarts preboil, then boil down to 5 quarts for your 1 gallon batch, guessing about a quart loss to trub etc.
The issue here is that your boiloff is very high, and your batch size is very small, so just do your best to finish your boil close to 4.5 to 5 quarts, add top up water either during the boil or at the end as needed to make batch size if you have trouble.