First, a warning -- I have never lived in a house that needed make-up air. Not even close. Double-pane glass makes little sense for us since all the heat goes around the sashes in our Victorian. My experience with MUA is related to commercial systems. What follows is an opinion about the kinds of things that would make me consider MUA. Unless you have a Code requirement for make-up air, you have a fireplace you use when cooking (I seem to remember that you are South Bay?), have a "naturally" vented gas appliance in "connected space" (no always-closed doors between the hood and the appliance), or have a "tight" house (recent, energy-efficient construction, most likely), I would skip MUA. Even if you do need MUA, the difference in the maximum hood flow probably wouldn't significantly influence the the cost of the MUA system, which I would think was primarily labor driven. If not significantly more expensive, and you can run at least an 8" duct (preferably a 10"), I'd go with 900 CFM for two reasons: * You have it when you need it -- guests over, and the kitchen fills with smoke... * A 900 CFM blower at 600 CFM may be noticeably quieter than a 600 CFM blower at 600 CFM The 24" will serve you well. Enjoy your new range!

Doh.. Just realized I screwed up my first post. Ment to post this in the appliances forum, not the kitchen forum. Oh well, hopefully someone can help me here. :) Ryan

Most ways of generating smoke are not "good" in the overall sense. For example, hot enough peanut oil makes nice smoke, but you won't want it on everything. Titanium tetra-chloride open to the air makes smoke, but it is pretty acrid and not recommended for breathing. Sulfur bombs for woodchuck harassment are another unpleasant option. The professional approach is to use schlieren photography of the rising heated air turbulence cells, but I would have to investigate the standard techniques used before I would suggest anyone try to set up a home recording scheme. Dry ice may be an option for observing air flow some purposes, particularly if the air is humid at the time of the experiment. The ice may need to be broken up to generate enough cold CO2 to cloud the air at the flow rate the hood should be able to achieve. Maybe just boiling water in a cool room will be sufficient to see the directions of flow. This technique, however, fails to measure the conditions that are relevant to cooking. To get a true measure of what happens with a hot pan generating a cooking plume with a meter/second upward and outward velocity distribution, schlieren photography is likely the only valid method of visualization, short of modeling it with computational fluid dynamics and presenting the results with time series imagery. ********** Schlieren photo of spillage due to insufficient air flow. (This is a commercial hood over a commercial griddle.) What is seen here are variations in the index of refraction of air due to the temperature variations from the heat input -- the same effect that causes atmospheric scintillation (star twinkle). Note that the inward air flow due to the ventilation blower cancels the normal outward expansion that would be to the right, but yet the momentum of the rising hot plume is too high to be completely contained and some of it reflects off of the baffles and other hood structures and leaks out of the hood. A companion photo (not shown here) shows that with significantly more blower air flow rate, all is captured and contained. ********* One might imagine from this example that with enough air flow, one can compensate for lack of sufficient hood overhang. This is true, but the cost in capital and electricity for the more powerful hood blower, along with comparable cost for the MUA blower, plus cost of MUA air heating or cooling as required (not to mention noise) makes this a non-optimal solution. kas

I have the largest heaviest Wolf hood hanging from an extension. I can relate that the extension is pretty hefty, and should be tied to real framing structure above it. (I suggest GRK type structural wood screws for good strength, at least in the corners.) The hood is then bolted to this extension as you note. I believe the hood would be difficult to bolt to it if it were necessary to put free nuts above the bolts. This is because the hood will have a sheet metal top. The nuts should be welded in place on the extension after alignment with the hood through holes, or if the steel is hefty enough, tap the steel. ("Only three threads matter.") I see no reason why your approach would not work, given minimal analysis or good experience in strength of materials. You will be trading time for money, and because you won't start out with the tooling required to assure alignment and fit, this time may be significant. This is the time to also plan the path of the duct through the framing. Installation of my hood required use of a hydraulic lift used for installing ceiling sheetrock, due the the weight of my hood and only two guys, one of which was me. I think four regular guys could hold it in place while a fifth inserted the bolts, or just the two guys who delivered my 48-inch Sub-Zero, but the latter pair would likely get angry if it took very long to get the bolt holes aligned for bolt insertion. Also, my peninsula not yet present. If one has to work above an existing counter, hood support and reach to the bolt locations may be difficult, or at least require some planning and temporary support structure. My delicate hood (made for Wolf by Independent): kas