Yeah even the best of intentions... plus a beer or two have caused me to forget watching at 200F+. For me I usually pull the lid at 206F.
Preboil volumes are a gallon per half hour. So for an 11G batch:
a. 60 minute boil = 13G preboil Volume
b. 90 minute boil = 14G preboil Volume
That is for a 100% manual mode boil on my electrical system with 5500W (so a good strong rolling boil). I have slowed that down my decreasing the heat applied. However getting a consistent boil volume is more important to me than saving .10 in electricity on a boil
Re: your question, do you mean 13G preboil volume? Or a 13G batch? (15-16G preboil for 60/90 boil times, respectively).
Basically the difference in the megapots in the
20 -
25 gallon pot is the 20 is 16 tall by 20 wide and the 25 is 20 tall by 20 wide. So a little less than an inch (.8) in wall height = 1g
If you watch it with a spray bottle handy you should be fine for a 13g preboil vol (gives you about 5.6 inches of wall to the top of the pot (for preboil volume of 15-16 gallon it gets a little tighter at 4-3.2 inhces of wall height). Not sure if you use an immersion chiller (I do), so that may factor in as well. Obviously the 25G gives 9.6''.