Its still in the planning stages, but my son wants to install a downdraft fireplace insert,with only about 12' of chimney above. Chimney will go in next week. Im worried there will not be enough draft. He mainly wants it for the fireplace look so could always run it in NON-EPA mode which lets the flue gas bypass the re burn chamber. I'm wondering if such a short span of chimney will create the needed draft for a downdraft stove. IF you figure the flue outlet is about 2 feet from the floor ,now you are down to 10' .