That will depend on your ash buildup. Many factory smokers have 1 1/2 to 2 inches and can get full of ash before you are done with your cook, causing the fire to starve for oxygen. When I made the grate for the fire box in my BSKD I think it was about 3 1/2 inches. Not sure, that was awhile ago. I burn pretty much all wood with no charcoal, and depending on the species of wood, that can create a lot of ash.