maybe someone is burning wood in their fires, or someone is cooking smoky foods. the chimney is used to that the smoke doesnt stay inside the house and exits through the chimney.
Hot air rises, just as cold air lays low (sinks) to the ground. When a fire ensues, smoke (the product of carbon combustion) rises with the hot air. Chimney design is what keeps smoke from just going...
It is a matter of common observation that furnaces in various factories are provided with very tall chimneys. Fresh air is drawn through a hole near the bottom end of furnace ,while smoke (being hot...