Just today I was 80 minutes into a 90 minute boil that seemed to be pretty tame. I have been using a fan to keep down the possibility of a boilover, didn't think to realize it was working, pulled the fan to put it away and came back to a boilover a doused flame. You think I would learn.
I would agree with this in my last apartment. That gas stovetop cranked! The one in our new (to us) house just barely gets 5 gallons to a boil. I strattle the pot between 2 burners to get her up to a boil.
That being said, I will likely have a boilover my next batch.
I agree, an unwatched pot ALWAYS boils over.. Fermcap, low flame, boilover fan, 45 minutes into the boil... doesn't matter. Two minutes to take a leak and you will have a half gallon on the floor.
+1 on turning down the flame. I reach my boil slowly and consistently. I usually heat while I'm doing my run-off, so it's near a boil when it's full and I can just feather it a little to get it where it needs to be.