a vent rather than a clean out? I was never aware of that, good Idea perhaps, but wonder how it would be kept clear and why the door at the basement is not louvered. Essentially, (I believe, perhaps mistakenly) it acts in the same manner as the identical clean out that is present on the oil flue. Other than some small leakage which may be coming from some very small areas around the unit there is no air coming from the basement whatsoever (it is plugged solid- which takes about 3 weeks perhaps to fill)). this leakage is consistent with what is exppected and required, in normal operation via the louvers on the door. Are you indicating that I am losing draft of creating more?
also, after shaking this morning I find some "chunky" white coals(more than not). Certainly not fine ash like a wood fire. Could close off the damper more (usually burn at 1/2 to 3/4 vent hole exposed) but, naturally, the more draft the more heat this thing puts out. Nut Coal