I don't know a number either and don't recall e.g. commercial hood manufacturer Greenheck addressing the point. Commercial systems usually run at fixed flow rates.

Baffles work by flowing the air around sharp bends and thereby centrifugally slinging the larger grease particles into the baffles. It seems to me that at some low air velocity this won't work well. A large hood at 300 cfm (less, really, given typical losses) might be low enough for the baffles to be ineffective at grease capture, although their function of fire stopping will still apply.

However, if 300 cfm is really OK for the cooking being performed, I wonder whether the amount of larger grease particles that would be present would be enough for this to matter.

In any case, low speed air passing through mesh filters (not to mention typically dirty mesh filters) will still mostly impinge on the mesh and deposit the larger grease particles.

kas

What would be enough the magic number that a person recommends? Anything over 300 I would need make up air here in WI. I have been waiting three weeks for my hvac guy to get me numbers on a make up air system for 1200cfm. Im guessing if I could get by with a system of maybe 600cfm, that could possibly be less expensive than then 1200 system.

Trying to get around the code requirement by putting in only a 300 CFM vent is like someone trying to build a 6 bedroom house where a septic is only zoned for a 3 bedroom, and calling 3 of the bedrooms "studys" to get around the code limitations that are there for your health and safety. You get problems with both scenarios.

300 CFM will barely ventilate a consumer grade 30" range. It really wouldn't even be enough for one of the higher grade consumer ranges, much less a pro style range. If you want the high BTU range, you have to have the CFM and makeup air that goes with it. Downsize the cooking products or upsize the budget to take care of the whole package.

This post was edited by GreenDesigns on Tue, Dec 3, 13 at 17:46