Why does smoke rise up a chimney?

Answer 1

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 anywhere around a fireplace. A chimney uses the principles of rising hot air and acts as funnel. A chimney's flue (the device which controls the amount of air drawn up the chimney) affects the funnel effect dramatically. As hot air rises up the chimney, the fire consumes more oxygen in the room where the fireplace is, creating a vacuum effect, which in turn feeds the flame with even more oxygen faster. It is the combination hot air rising and subsequent vacuum effect in the room below which ensures that smoke from a fireplace fire will go up a chimney. ithout the control of the chimney flue, this effect could quickly lead to a fireplace fire getting too hot for the fireplace to handle.

This effect can also be extremely dangerous in a house fire or a building fire in which there are drop ceilings. Some natural building areas, such as stairwells, act as natural chimneys. In office buildings with drop ceilings, it is against fire codes to have any drop ceiling tiles removed, as this can cause a chimney effect if a fire were to break out. Remember since a chimney effect leads to oxygen been fed to a fire at faster rates, the fire can quickly accelerate and consume an area.