Was slow to get going. Flamed up nice with vent wide open and door cracked open. When door is closed tight flames die out rather quickly with vent open . Is this normal? My stove pipe goes up 3 feet,out 3 feet through the wall,then up 10 feet. Roof is 12/12 pitch.Top of pipe is 7 horizontal feet from roof but still 7 feet below the peak.Any help would be great.