Short of climbing up to look down, a house has two terra cotta flues a larger one for the fireplace and a smaller one that doesn't seem to come down anywhere i can figure other than the wood storage area. (Yes i looked in the basement and on the second floor and in the garage) Is there any chance that the wood storage area has make-up air? When I look up at that spot, there are some wooden slats above that are fairly tight (i.e. I can't see past them but maybe a quarter's width apart). Surely someone on here has a similar type setup.