Question: We recently purchased a cabin with an open masonry fireplace and masonry chimney. †The chimney had been lined with two ceramic (clay) flues. †Upon inspection, the chimney and flues looked good so we started a fire. †After a short time we noticed smoke entering the room from the attic. †We have always had woodstoves but are unfamiliar with fireplaces. †My questions are: 1. Are we correct to assume that there may be a crack in one of the clay flues causing the smoke problem? 2. When calculating proper chimney capacity - do we add the sizes of the two flues together? 3. Can we correct this problem by lining each flue with a new metal flue? Answer: There is virtually no such thing as a clay flue or chimney that does not have some amount of small cracks that might let smoke escape. However, usually an upward draft assures that such pin holes such air IN rather than let smoke out. You mentioned that the one fireplace has a doubel flue? If so, this can be bad news in my experience. I have seen smoke come out the top of one and go down the other! A circulation of this type can really mess with the draft. One possible solution is to make certain that the two flues terminate at different levels, that is raise one of the them up somewhat and see if that makes a difference. If nothing else works, you might even want to try closing one of them off, as it may be doing more harm than good.