To keep smoke from entering a room, turn off kitchen and bathroom exhaust fans and close forced air heating registers that are near the fireplace. If the chimney serves a stove, move the stove closer to the chimney and eliminate elbows in the stovepipe connector. If the chimney serves a fireplace, the only solution may be to make the fireplace opening smaller. This can be done by raising the hearth or installing a canopy hood down from the top of the fireplace opening. Prefabricated chimneys can be made taller by adding another section or two.
Weather stripping or otherwise sealing upstairs windows and attic doors can help.
If you tried these remedies and smoking still occurs, the only remedies are either a smaller stove or fireplace, or a new chimney. Increasing the diameter of the chimney is the surest way to get more capacity. Problem Smoke coming out of stove while first starting up in cold weather. Cause Temperature differential between outdoors and indoors causing changes in air movement in the house to equalize that of the outside pressure. Provide a separate air inlet.