I don`t see much in print (talk) regarding the necessity and benefit of combustion air being drawn from outdoors for pellet stoves. Looking at my Harman P38 intake air flapper being 1/2 open and pulling in a considerable amount of indoor air I would think that a separate outdoor air supply would be a must do item since the stove would otherwise be contributing to indoor negative house pressure not to mention the heat loss somewhat akin to burning in a fireplace. Comments and thoughts appreciated. John OK , I did a search and found some discussion on this. It seems it`s a trade off with the colder combustion air effecting the burn efficiency .