Very Specific Hood Query - please help!!
We are installing a 36" Capital Culinarian AG range with four burners and a grill in an island. (I know it would be better against a wall, but it's impossible). We had planned on installing a 42" hood with an internal blower running 900 - 1200 CFM's. It will be about 30" above the range top and vents directly up through the roof (which is sloping but at the very highest point, just about 9'. The problem is that our existing duct is 8" and we've been told you can't run anything more powerful than 700 CFM's through an 8" duct.
Our house is quite old with structural beams in the pitched ceiling that are no way up to present day code. If we enlarge the existing duct to the 10" that would be required for the higher CFM, we'll be cutting into beams and opening up a whole can of worms with inspectors. Our contractor is advising (pleading/warning?) us to stay with the 8" duct.
So my question to the experts out there is will 700 CFM's be enough? It doesn't have to be perfect but it has to be functional enough to be able to use the grill. Or is there another possibility? Can you run something more powerful through the 8" duct? If so, any brand suggestions would be much appreciated.