I just answered this question to a gentleman and figured it might help some here - feel free to print out, edit, etc. - Posting elsewhere is oK with credits.:
Well, stack effect is just a catch-all!
Let’t break it down:
1. Chimney smokes when starting
This is classic “flow reversal” which means the chimney draws down instead of up when not is use. This can happen either ALL the time or part of the time.
In general, the solution to this one is easy. It has mostly to do with the technique in starting a fire.
see the last paragraph at:
http://hearth.com/what/chimney.html
and the article on starting a fire that it links to.
2. Chimney Smokes all the time
In general, this is too short of a chimney, or too big of a fireplace! Chimneys should have at least 14 feet of height, and preferably more, above the damper.
Numerous ways to solve this and it is usually good to do more than one fix.
a. raise chimney
b. lower opening a little (called a “smoke guard")
c. Use grate and keep grate near rear wall.
3. Fireplace smokes on windy days - This usually means chimney is in cross winds. Raising the chimney or putting on a special “wind helper” cap can help this.
4. Two or more chimneys in the same structure, but house smells when one is used.
This can be “smoke crossover” from one flue to the other - smoke comes out one flue and is sucked down the other - you can easily solve this by raising one flue as per the URL below:
http://www.extendacap.com
--
Craig Issod
ExtendaFlue Corporation
http://www.extendaflue.com
http://www.extendacap.com
