If there is not enough air supply, the pellets will usually turn black... charcoal... If you have a fine layer of white (ish) ash, you've got enough air supply.... The correct amount of air also helps to burn off any creosote... so your food has a nice golden color to it and a great flavor... or something like that....
I use the vent holes not only to supply air for the
AMNPS, but I use them to regulate the amount of air through the smoker.... The 3 holes I have in my MB mod are 3/4".... with the heat on in the MES, there is REALLY good air flow... I like lots of air flowing through the smoker.... I think the food tastes "cleaner".... what ever that is... I prefer the taste... I have plugged the upper hole and it does something different to the smoke and the flavor... so now I smoke with all three open....