My smoker(which is pictured in my avatar) has an offset firebox which is rectangular and quite large. It has a grate with bars a couple inches apart. When I get a good fire going the temp will remain constant for around 40 minutes and then the coals start to slip through the grate and land in the ash. I am then left with a piece of wood which many times starts to burn out since I don't have any coals under it. I have to stay on top of it constantly and feed the fire often to prevent this from happening. I suspect when the coals fall through they get smothered by the ash and I am losing heat from them also. Has anyone used a firebox which has two grates? The grate on top for burning wood and the grate below for catching the coles and keeping them out of the ash. I feel as if I am not getting enough heat from my coals before they fall through the grate and land in ash. Of course I do clean out my firebox before each cook but it doesn't long for the ash to build up. Any input on this from others would be appreciated.