You know, I have had that same dilemma with my HERMS system and I have 3 20 gallon kettles. Most times, if I do a big brew, I just do a 5 or 10 gallon batch. Even with the 10 gallon batch, there is sufficient room. Most regular beers (OG 1.040 to 1.060), I could easily use a 15 gallon kettle...