Devil505 wrote:Here's my "layman's" understanding of how a chimney works:
Warm air rises
As the warm air rises it expands
Trapped within a chimney's walls, this air expansion is "squeezed" & since it wants to expand (but is prevented from doing so) it increases it's velocity upward to escape it's bounds
This increase in upward velocity creates a vacuum below the upward rushing air.
Since nature abhors a vacuum, it (nature) fills it (the vacuum) by sucking the exhaust out of the fireplace/stove/furnace
The higher the chimney, the greater the upward air velocity & vacuum
Thus, we have Draft!
Any engineers out there wanna critique my analysis?
So the question is: Is there a minimum height necessary to achieve this chimney effect, & if so.......how does one formulate it?
Yes warm air rises because its lighter but actually a chimney should work without the warm air rising thing. The reason being is that it works not because of air temperature, but air pressure. At the bottom of a 30' tall chimney, let's say the air pressure is 14.7 PPSI. Now if you climb the chimney, you may find that the air pressure only produces about 14.4 PPSI Because there is 30' less air squeezing it down. The draft is created by a long cylinder seeking to equalize pressure through out its length. So any long length of pipe stood up should create a draft of sorts even without a fire. It's Bernoulli's law!
It's the engineer in me.