Just a bit of advice on the boil off rate. Figure your rate in gallons per hour rather than a percentage. As long as you are using the same pot and the same intensity of flame you will boil off the same volume in an hour regardless of whether you are boiling 3 gallons or 15 gallons. Obviously, the percentage will vary widely between these two examples but the volume boiled off will be the same.
If you boil off rate is one gallon per hour (a very common figure) you simply add one gallon to your desired post boil volume (plus whatever volume you normally leave in the kettle after the boil).
My boil off rate is 1.5 gallons per hour. I normally leave about 1/2 gallon of wort behind in the pot (absorbed by hops and mixed with break material). In order to get 5 gallons into the fermenter I start with 7 gallons of wort pre boil. (1.5 plus .5 plus 5.0)
Wayne
