[TheForge] Something I've forgotten or worse yes I just imagine I once knew.

[Charles]

For Gas Vent

http://www.hartandcooley.com/assets/files/c3/hart-cooleytypebgasventall-sizing_guide.pdf



And of course building codes will give guidance as well.... Here is 2005 ICC

http://www2.iccsafe.org/states/new_york/NY_FuelGas/PDFs/Chapter%205.pdf


Charles

________________________________
 From: "wmullett at bright.net" <wmullett at bright.net>


I think that rule of thumb would be invalid.  Besides chimney area and height, the draw of a chimney is also dependent on exhaust temperature and the temperature of the flue.  A flue that is mostly exterior may cool too quickly to maintain a suitable draft.