Yes, lump will burn down more than briquets in the chimney since it's a hotter fire and the fuel isn't as dense. Even still, I find that 1 chimney of lump is usually enough to grill dinner for my family of 4. Personally, I would never cover 100% of the bottom of the grill with coals because I like to maintain a safe cool zone that I can move food too if need be. Sometimes I use the warning rack for this, but being able to move food to different heat zones is definitely an advantage in turning out good food. All that said, I have 3 and on occasion use them all when I have both of my 22 1/2" kettle going.