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.

A bathroom fan duct may be only 4- or 6-inches in diameter, whereas a kitchen hood duct for a system that works for your size hood needs to be at least 8 inches for good flow. The bathroom duct may be aluminum or PVC, the hood duct must be steel. I doubt that combining the two functions into a single duct would even pass code requirements. Venting to a patio strikes me as moving the odor outside to the one location you don't want it. Search this forum for make-up air related topics to begin. It is possible to get away with a controlled damper "hole in the wall" under some conditions. We can discuss your questions further once you have some basic understanding. Grease and water vapor laden cooking effluent plumes, whether odoriferous or bland, have to be captured and contained by the ventilation system. I recommend a flow rate of 90 CFM per square foot of hood aperture. For any reasonable duct length, hood filter restriction, and imperfect MUA, assume that the blower's rated CFM has to be 1.5 x higher. This subject is also treated here extensively. Kitchen renovation is a really big project with many conflicting demands. It requires a lot of research to match one's goals with the available space and funding. Do not scrimp on the research. Layout, appliances, cabinets, plumbing, power, lights, .... the list is very long and may lead to recursive design as more is discovered about all the interacting subjects. Try to avoid a divorce. :) Good luck! kas

In order to begin to understand it, you would need to buy ANSI Z21.1 for about $650. There is some very technical engineering, even though it doesn't look like it, in the ventilation between walls of the oven and cooktop sides that ensures that the cabinets up against the range will not get hotter than 194°F. If you block the airflow by lowering the range (some people try modifying the feet for thin countertops that make them less than 36" tall), or putting ducts in for MUA, the outside wall of the range will get hotter. If you force that much extra air through the range, (push or pull) you change the way the gas burns, and create CO problems. Even if you can adjust the air shutters to compensate, you would then have to turn on the entire system just to make a pot of tea, in order to get enough air to get a clean burn. With holes in the floor or back wall, the natural draft intended/engineered to cool the outer walls of the range can be disrupted or diverted, leaving the heat to build up around the range - nothing to do with heat in other areas of the home. What can't tolerate more heat than the wood cabinets around the range? Another separate reason for no holes is the possibility of a gas leak. How much gas do you think that duct will hold, just waiting for someone to create a spark? The testing standards do not say no holes "unless someone thinks of some unusual excuse".