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

[CGRAF]

Somewhere in the dark recesses I seem to remember a rule of thumb for 
guesstimating CFM of a flue.

It was something like 2X ( cross section X Height)   So a 10ft stack 
with a 81 inch cross section would yield about 1600cfm .

I believe this was for a gas or oil fire furnace. I am certain a wood or 
coal fire would have a different yield due to the lift supplied by the 
heat being greater.

Anybody able to help me out?

Mike Graf