[wlively]

Do a search for chimmney on the forum. I posted a couple of links that deal with this and two of them were technical with formulas.

Basically the higher the chimney height the higher the pressure differential, ie. the better the draw. You can compensate somewhat by increasing the size but once you get below a certain height it probably wouldn't make much difference.

Sorry, I haven't crunched the numbers. I finished mine before I found the links. I have a 42" pompeii and a 36" high (12" transition + 24" Duratech 8" dia) and mine draws plenty well.