Smoke Accumulates in House from Wood Burning Fireplace?

I have an wood burning fireplace insert (metal tube for smoke to exit). The fireplace is in our den with a 10 foot ceiling. Smoke accumulates in the house, especially in our adjacent bedroom with an 8' ceiling. I am burning seasoned wood that was cut this past summer (does it need to be seasoned longer?). I have had the chimney (pipe type) cleaned by a professional chimney sweep recently. The flue is open! What could be the problem? Thanks in advance!

By Ellis