In an effort to know how much water I need for an upcoming small batch no sparge BIAB I want to know how much water I need. I haven't started messing around with Beer Smith so forgive me if this info is there.That's an OK place to start for boiloff. You're going to have to brew a few batches and dial it in from there. Your absorption may be significantly lower depending on mash thickness and how hard you squeeze your bag. A typical recipe for me may be in the 6lb of grain ballpark, and I typically lose about a quart to the grains.
Is it safe to assume .1 gallons per pound of grain absorbed and roughly a gallon per hour of boiling?