What goes up a chimney down but won't go down the chimney up?

Answer 1

Smoke can go either up or down a chimney. In order for smoke to go up a chimney, or draw correctly, there must be replacement air coming into the fireplace from the room, and therefore replacement air must be coming into the room. If there isn't any replacement air, the air pressure in the room will drop, and if the air pressure gets below that of the outside air at the top of the chimney, the smoke will be drawn to the lower pressure area of the room, down the chimney.

Answer 2

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. without 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.

Answer 3

An umbrella