what i was referring too is that some folks claim with a longer chimney they get more draft. when your stoves blower is not in operation (when your stove is at idle) the extra draft may pull air in around a door or through yoru blower when it normally wouldn't with a short chimney. if this were to happen you could get boileover. if you were to add the barometric flapper, that would control your draft. this draft control could keep your actual draft on the stove the same (or very close too) as it was when your chimney was shorter