Smoke from my fire place choking me out.? I have a double sided fire place contained by my house and...

I have a double sided fire place contained by my house and when I have a fire the smoke billows out of the fire place innards my house. It is the worst when I start the fire and also when the fire dies down, even after its been burning for hours. The flue is cavernous open and the chimmney is completely clean. Am I missing something, is in that anything I can try. Any advice would be apreciated.
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Answers:    get any tall trees essential the chimney top...sometimes they can create a downdraft...
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A couple things to check. One is the chimney height. It may be too low. Normally, 3' better than the nearest roof peak is advisable (and sometimes code). This help prevent down drafts. You may also have a outstandingly "tight" house. Try opening a pane just a bit when operating it. This can create "draft" to assist the smke to exit through the chimney. When lighting it, hold a piece of burning quality newspaper up into the flue for a minute to start the draft.