[turbo6bar]

Residential duct sizing is covered in ACCA's Manual D. Using recommended maximums for return ductwork (your make-up air), the minimum duct size would be 14" round for 700 CFM. However, this is with an HVAC blower fan pulling air. If you want the make-up air passive flow, the duct would need to be huge so that MUA is not pulled from the house.. It might be preferable to do as suggested, and make the area positive pressure with an axial fan. Fantech and Elicent make axial fans that would work for this application.

I don't do this stuff for a living, but I don't see why your make up air duct could not be sufficiently placed so that your vent hood pulls most flow from the MUA and little from the house.

Also, you should test system performance as related to hood height. As the hood moves closer to the range, you'll need fewer CFMs.

My intuition (could be bass ackwards) thinks MUA ducts in the wall on either side of the range would create a crossdraft carrying smoke over and up.

The other concern is if you have fan providing MUA, you now have a great source of air for combustion. This would not be a good place for a grease fire.

I would search the forums at greenbuildingadvisor.com and jlconline.com. Gotta get to work on the fixer-upper now. Will do some hunting later if you don't find a solution quickly.