Stack Effect is the movement of air into and out of buildings, driven by air pressure, temperature differential, and moisture.
Buildings leak air through walls, interior and exterior, ceilings, crawl spaces, basements, and attics. This movement of air will result in warm air rising in a space forcing a higher air pressure at the highest points in your home. During the heating season, the warmer air riser through a building and escapes through attic access, recessed lights, ventilated attics, unsealed ducts, and top wall plates. 
The rising warm air pulls cooler air in behind it from outside – through crawl spaces, basement, rim board, bottom wall plate, windows, and doors. Air infiltration is a huge concern in a building as it contributes to comfort issues (drafts), moisture, and higher electric bills. On the other hand, using stack effect in a high performance home to your advantage can help cool your home in the summer months. Creating a solar chimney forms a nature powered air conditioner. 
