The functions of a ventilation hood system are capture and containment of the rising effluent plume from a cooking surface and (where applicable) combustion products. Easily said but often ideal capture and containment are in conflict with available space, sight lines, tolerable noise, acceptable appearance, and affordable cost. So the OP's question might be rephrased as: How much of each of A - H is enough to achieve the OP's maximum tolerance for odor and grease. Unfortunately, we can't know that tolerance, and hence can't apply it to establishing a balanced system. Another approach is to start from basics. 1) Establish the cook top configuration and the sizes of pans that would be used on the cooktop. 2) Sketch from a side view and a front view the rising effluent plumes from these pans. Assume that the expansion is in the 20 - 25 degree half angle range from the edges of the pans cooking surface or edges if gas fired. Effluent hitting cabinet sides or the back wall is assumed to be directed at the hood. 3) In concert with choosing a hood depth and width that encompasses the effluent, establish a hood height that doesn't block one's view of the pans or provide a (one-time only, one poster noted) skull impact when bending over. Higher generally requires deeper, but also improves the view and safety. Note that in flat bottomed hood configurations (filters flush with the base) only the filter size counts as the hood size. Otherwise, the inside aperture of the hood counts as the hood size. 4) Choose an aesthetically tolerable design. 5) Determine the filter area (square feet) of the hood and multiply by 3 ft/second for effluent rate of rise and by 60 seconds per minute. The result will be the minimum full power air flow (cubic feet per minute) needed at the filters. (This is all approximate). Achieving this may require an exhaust blower rated 1.5X larger due to various pressure losses. 6) Given this flow rate (cfm), divide by 1000 ft/min, and also divide the cfm by 2000 ft/min. This is the duct cross-section area min-max range to strive for to keep unfiltered grease particulates from condensing on the duct. As always, a given duct diameter relates to duct cross section by A = (pi*D^2)/4. where the diameter D has to be in feet. (Those who are metrically oriented can make the appropriate transformations.) (There are many rules of thumb for required flow rate, but they often presume certain hood characteristics, such as conventional commercial design. The Wolf design guide has suggested fans to use with their hoods based on their estimate of what is adequate.) Second order effects may come into play as one decides whether the result of the above is affordable or installable. For example, over specifying the fan may allow the hood to appear slightly larger, improving capture. Or a conscious decision to cook the greasiest most odoriferous food only under the center of the hood might be made to reduce effluent escape from a hood that is otherwise too small. kas

I stay out of these things most times but if I were talking to a client of mine (or my wife) First- I'd suggest not to do a mantle hood as narrow you have pictured. But if you must go that way then ditto to what green said. I typically advise to keep a keen on the total budget and do NOT look at the cost of any individual item until it comes time to trim the budget. Everything anyone "wants" is expensive when viewed without context. The question becomes can it fit in your budget, is it important enough. Next- avoid poor imitations- if you can't get the specific thing to look right then let it go-completely. A lousy imitation looks like one (ala the LWO thread) Instead if your trying to generate more interest do it another way, or somewhere else. Most folks are happier with less done well than more done poorly. You only need one or two things that make your heart sing every time you go in the room years down the road. Often those are small things, smaller than what people focus on during the process.

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

Well, let's see if I'm up to four questions all at once. Rule no. 1, do not believe VaH sales persons trying to explain blower operation unless you have some other means of determining their veracity, and most importantly, their understanding of the fluid dynamics of air. Rule no. 2. Blowers that suck air also blow air and cannot know what is the cause of the pressure differential across the blades, at least at the tiny pressure differences that apply to hood blowers. Pulling air could be a problem when the intake is at feet of water column reduced pressure, not inches. This does not mean that the blowers will be unaffected by operating into a duct bend, or from a hood transition, etc., but in general, even a VaH blower is pulling air from one side and pushing with the other side, and its blower, like all others, is constructed for one direction of air flow and to achieve a particular flow rate performance at a tolerable sound pressure level. I don't keep up with VaH, but I thought that their 1200 CFM (claimed) hood had two 600 CFM blowers, not four 300 CFM blowers. Perhaps they are using two motors, each with two cages. Fan blade tip noise is caused by the turbulence of the air spilling from the blade tip. It results from operating at a high speed exacerbated by spilling from a crude airfoil shape. Casablanca ceiling fans move a lot of air but the turbulence is at most modest due to the low speed of each blade tip. Duct noise is from irregular air flow in ducts. It generally won't be laminar at the flow rates of interest (1000 - 2000 ft/min). Pressure loss of bends is the result of degrading the flow due to increased side wall interaction as the moving air tries to pile into the blockage ahead before turning. Smoother longer turns reduce the effect. VaH Magic Lung blowers use squirrel cage designs that are good, I guess, for throwing grease at the hood walls, but have a weakness -- they don't like added pressure loss relative to some other popular fan configurations, such as axial in-line blowers or centrifugal carousel types such as Wolf/Broan/Abbaka roof blowers, so actual flow due to inadequate MUA or constrictive ducting will have a greater effect on actual flow rate than these other designs. It is certainly possible to build an external chase for ducting and even for the silencer (about 4 inches larger in diameter). Number of bends is worth minimizing, but it is always possible to specify a blower to provide the needed flow rate at a given pressure loss if the bend number cannot be minimized. Roof blowers usually also work mounted on walls. One secondary effect is that on roofs, sunlight UV generally degrades and eliminates any grease that condenses on the blades and is expelled onto the shingles, whereas on siding that is in shade the grease may become noticeable. Commercial blowers operated in up-blast or side-blast configurations likely will not blow grease onto house surfaces, but condensation within the unit may lead to some release around the unit. Downward ducting has a couple of deficiencies. The process of turning a rising plume to a downward direction requires additional energy (equivalent to pressure loss) and likely causes the grease particulates that escape the baffles to condense by impingement early rather than being expelled. To keep the typically long horizontal underfloor duct path from dripping, a continuous down tilt will be desirable, and in a typical basement this may lead to requiring a hole in concrete rather than in a wood wall. Some municipalities may not approve such paths. The "heat rising" view is probably less relevant because the duct velocity will be at least 10X the velocity of the intake to the hood. Last, an observation. My hood blower is rated for 1500 CFM and is roof mounted. Actual flow into my hood is about 1000 CFM with presently passive MUA. This is 100 ft/min air flow across the hood entry aperture. I have a 10-inch duct with LD-10 silencer. Flow is 1800 ft/min in the duct. There are three bends, all less than 90 degrees to get the vertical hood direction to a shallower direction in my attic that encompasses the silencer, then two more partial turns to match the roof blower's intake angle. Note that configurations of this type not only allow room for the silencer, but also allow the hood exhaust to be placed more optimally on the roof, if needed, than exactly above the hood. I hear mainly baffle hiss at the cooktop, with a slight underlying rumble, likely due to imperfect fan carousel balance interacting with imperfectly stiff roof planking. Edit: I feel comfortable asserting the baffle pressure loss, and MUA pressure loss, dominates all the pressure losses in my duct path. tl;dr: An external blower downstream from a silencer will always be quieter than a blower in the hood for a given flow rate so long as the external blower is not constrained to being significantly smaller than the in-hood blower. Other noise will depend on whether the baffle size and shape is reasonable for the air flow rate and the duct size is such that the air flow in the duct is in the range of 1000 to 2000 ft/min. Let me know what I forgot to answer.