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I don't have amy holes on the bottom of the coffee can, too much ash would fall out and into/onto the burner area. The holes are 3/8 in. and I have about 5 rows of them, all the way down to the bottom lip, I haven't had any flare-ups, so I haven't had to cover the can. I do get some ash droppings when moving the can in and out, but that's why I use the wet/dry vac.