Scott, just to elaborate on the concern I mentioned in the KF thread - that fan is rated 2,000 CFM, I see you've sized the MUA ducting accordingly, so you must be planning to use all of that flow. A 14 inch duct is about 1 sq foot, means at 2,000 CFM air will be moving through the MUA duct at 2,000 ft/min or 33 ft/sec. That seems very high, maybe too high to be realistic for passive airflow. There will be plenty of friction resistance in that 1 sq foot ductwork, and there are plenty of other ways air can flow into the kitchen through 18 sq foot openings (the doors to the kitchen), so why are you confident you'll pull air from the passive MUA rather than from the rest of the house? Suppose you do get that much airflow through the MUA duct, say with a fan. That is 2,000 CFM entering the space under the range at initially 33 ft/sec. If the space is 6" high by 48" wide i.e. that is 2 sq feet, so you can figure the air has to exit at 16 ft/sec, even if you use baffles to slow down the direct blast. That might ''blow your socks off'' or at least give you frost-bitten toes. And, will air exiting from the under-range space at that velocity and in a horizontal direction, will it really turn sharply to head up into the vent hood? Perhaps it will simply spread a frigid floor-level layer of air throughout the kitchen, while warm room air gets sucked out the vent hood. 2,000 cubic feet per minute of it. Finally, the lesson I got from that article I linked you to, in the other thread, is that turbulence and cross-flow make vent hoods less effective. That is, I think, why the article says to introduce MUA from various locations including some far away from the vent hood. So you get a smooth airflow into the hood. That's something to think about too. I imagine that fan won't actually flow 2,000 CFM in a real world vent hood, so these numbers are a worst-case, you'd recalculate using realistic outflow rate - but anyway you see my concerns.

I think that the OP is on the right track. The make-up air should be as close to the appliance as reasonably possible. That is the way MUA should work for other combustion appliances like water heaters, furnaces, boilers and fireplaces. You don't want unnecessary air changes in the rest of the house or even in the rest of the kitchen just to remove smoke, combustion gas and aerosols from the cook surface. That is just wrong-minded. Opening a window or door is not acceptable because it is too dependent on which way the wind is blowing at that moment. In laboratory design, a number of years ago, the design of fume hoods took a major turn. They used to just suck ambient interior air, a lot of it, up the stack. 20-30 years ago, for a spell, they just started incorporating raw MUA into the hood design. When working in those wonders you are definitely aware of the outside weather because outside air is moving directly over the person working in front of the sash and everything in the hood was exposed to outdoor air conditions. It was a big energy savings, but not so good for the laboratory scientists and their work in some cases. Now there are other solutions. If you are having trouble envisioning what a fume hood looks like, just google it. You will get lots of hits. I sometimes wish I had one at home for cutting onions ;-) Rather than putting the MUA far away from the range it should be as close to the range as possible. The heck with MUA under the range. From my point of view, a lab guy, the most efficient way to build a MUA system would be for the range manufacturers to incorporate MUA into the range design like those now-outdated fume hoods. MUA should probably be supplied all the way around the perimeter of the horizontal surface. As a cook, I can say that I would not want it to be a simple opening around the range surface because that would be a maintenance nightmare. I expect that it might be best located somewhat lower than the horizontal surface in a way that it is easy to clean and does not get spilled into. A system like that would make for a comfortable cook and energy efficiency. The drawbacks of the now-outdated fume hood designs really would not apply to a range/hood system. In those, what you were working on could be very toxic and the process temperature-sensitive. In the case of a kitchen, the design can be a little more loose as far as allowing trace "fumes" from the stove to escape. What you are working on is not temperature-sensitive in the same way as a laboratory procedure.

First, this is what the proper calculations would say about Risinger's installation. OR THIS Second, short circuiting a hood, air curtains, and generally any makeup air introduced too close to the range will produce counterproductive turbulence that will reduce the effectiveness of the hood to the point that he may as well have just put in a 400 CFM fan without makeup air. Third, the floor under the range is required to be sealed from drafts on most ranges. But, you can't usually shove ALL that air through the HVAC system either

The only air that will flow out of the hood is that air that can enter the kitchen, so MUA is always necessary. The question is whether accidental MUA is sufficient, or is deliberate MUA needed. Generally at the 300 CFM level (which is more likely a modest 200 CFM actual flow rate), house leakage is deemed adequate for MUA unless the house is very well sealed. I you have combustion appliances, I would keep an eye on back-drafting when the hood blower is running and the house is closed up. A CO sensor may be desirable. Your municipality code enforcement officer can provide information on what regulations are being imposed.