I just finished struggling with the same issue. There seems to be a great deal of controversy about the magiclung and the ease of cleaning. I have spoken to some owners and they love them. As to their claim of their 600CFM being equal to other baffle or screen filter hoods rated at 900 CFM that appears to be valid based on two factors. First, there is at least a 20% loss due to the filters and second, many other units use a 7" or 6" duct further reducing their effective rate while VAH uses an 8" duct. All of these numbers are ideals that are never achieved in real world application so you have to take them as relative comparisons and not much more. I finally chose the Modern-Air duct as the best compromise as it uses an 8" duct, has an excellent reputation (made here in CA where I live) and very high quality construction and polished baffles with smooth rather than sharp edges. It was a little less than the VAH though that was not the deciding factor.

Love mine. Reinstalled it during my renovation. Go on line for information at Vent-A-Hood. Easy to clean after you have done it once.

I take exception to being called a collectivist. 8-) I guess I should inject the possibility of having the duct pass the second floor in a chase, perhaps located in a closet, an extra wide wall partition, or perhaps outside, allowing a roof blower. This should reduce noise a bit in the kitchen, and in the region of the side of the house where the duct exits. Note that a wall cap may approach the size of a wall-mounted blower housing if the cap is to have free flow. With a larger chase, even a silencer is possible. I haven't audited either the Best of VaH examples so I can't comment on their sound levels. An earlier VaH example (ca. 2007) was measured by clinresga vs. a conventional hood/blower and found to be louder. Functionally, my preference is toward whatever design best approximates commercial designs. kas

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.