In my experience - it isn't so much a function of BTUs but matching your pot to your burner size. You can have a huge burner, but if all that heat is blowing around the pot - it is completely wasted. I think the Blichmann is 72,000 BTU - and it has good shielding around the burner. I throw up a couple of pieces of sheet metal around the burner when in operation and I get >6 batches out of a tank. It does well enough that I don't even really pay attention to how many batches a tank lasts anymore - just cycle in a spare tank on the rare occasion that I run out.