weird to add to this old thread, but i wanted to add som other data... @clinresga: i wish i had read your post when i was trying to sort this all out last year...but fortunately, i think i ended up in the right place. i'll be upfront before providing more info: i am happy with my Ventahood. if i had the option of a remote blower, there is no question, i would have considered it, but in replacing an under the cabinet, microwave combo unit, the Ventahood one because of it's quietness at realistic speeds. anyway, i wanted to add the numbers i had recorded from a previous email to a friend last year when i ran into the imfamous "sticking flap" problem. (i'd be happy to elaborate on that if people want to know more about it) what i found (when the flap problem was corrected), using my Radio Shack meter at cooking location in front of the hood: Fan1 low: 57db (150 cfm) Fan1 high: 65 db (300 cfm) Fan2 high: 64 db (300 cfm) Fan 1 and Fan 2 on high: 67 db (600 cfm) as you can see, my numbers aren't too far off what was previously reported except for the lowest fan speed which is much quieter. nevertheless, i have to say that i often run Fan2 not only because of it's slightly lower volume objectively, but my subjective preference for the "whiter noise" nature of that blower. in fact, without the sound level meter, i had first thought oddly that a full 600cfm on was quieter than the fan1 on full speed on its own. i looked into a few other units including a Kobe, a Broan, and a couple other powerful "chinese hoods" that was crazy quiet at low speeds, but much louder to my ears (in the showroom) than the Ventahood. in short, i think some of the disagreement in VAH comes down to: - subjectiveness - stuck flaps - inproper ducting. (ie, installing it on a 6" or smaller duct) btw, i don't buy the whole Magic Lung giving me 900 effective cfm necessarily, but this is true from experience: the 300 cfm (one fan on full) pulls out much odor than our supposed turboboosted microwave hood did at its 420 cfm rating...i would guess the Ventahood at 150cfm still bests it! not all cfm are created equal when specified by the manufacturer :)

If you are concerned about noise, consider one that has a remote blower motor. I have a 900 cfm Broan and my blower is mounted on the roof (you can also mount them on an outside wall or in-line). My floor plan is very open. If it's running on high (never necessary) and I am standing next to it, I can't hear the TV in the living room. But anyone in the living room watching the TV can hear it just fine. The noise I hear is not the motor, but the air moving through the mesh screens and the pipe. Most of that noise will be reduced or eliminated when I insulate and box in my pipe with a chase and replace the mesh panels with baffles. Since the motor is adjustable, I usually run it very low and can hear the TV just fine over it.

Mine is from builder. It is one of Thermolec air heaters ( http://www.thermolec.com/en/productView.aspx?type=product&id=77) plus a separate current triggered flapper. The heater tries to heat the air to 15 C (PWM), activated by the air flow. It is a passive one and connects to the air return of the furnace via a 10 inch duct. It is not as sophisticated and highly performed as Kas's.

Magic is often over valued in real life, if not in anime. Historical views on the subjects raised by the OP can be found in this forum's archive by searching the key words. I will agree with anyone who notes that doing so can be tedious, albeit informational, due to the large body of commentary in these areas that has accumulated since at least 2007. Generally, the dominant noise in a simple blower-hood-duct system is the turbulence noise from the blower blade tips. This is true for VaH squirrel cage blowers as well as various other blower configurations. Baffle turbulence noise is secondary and is normally a hiss like sound, although this may vary with the quality of the baffles. (Air speed across the baffle edges is always going to be lower than at the blower blade tips due to the difference in areas.) Using an exterior blower with an intermediate silencer (muffler) reduces the major part of the blade tip noise, leaving only the baffle noise and some hood side duct noise. This allows conversation across the hood and is recognized as a noise solution. Where a silencer is not used, an exposed VaH blower vs. an internal-to-the-hood conventional blower may have modestly different sound levels. The purchaser will need to audit the candidate systems to truly know which is perceptibly louder. While VaH assert a factor of 1.5 in effective flow rate, this appears to be because there would be flow rate loss of that order if they had pressure loss from baffles due to the slope of their fan curve. Normal blower configurations can have a 1.5X like drop with baffles, ducting, hood transitions, and MUA pressure losses all included. VaH do not count most of these non-baffle sources of pressure loss, and hence will flow even less than their specified flow rate in a real physical installation, just as conventional configurations do. In a not too far back argument here, it was clear than once all the losses were considered, "conventional" blowers were better at dealing with the usual significant pressure losses that are likely to be present in a real system. VaH fan curve data can be compared with comparable Broan fan curve data (to pick on one source) to see which has the more desirable closer-to-vertical behavior when reacting to pressure losses. But to know the actual net impact on one vs. another, one has to estimate all the losses and then use the different curves to find the estimated flow rates. VaH cleaning convenience vs. baffle cleaning convenience has also been argued here, with varying opinions about VaH. As I don't have a VaH I can only direct the OP to the archives or to others who may join this thread. In fairness it is necessary to point out that VaH, like other manufacturers, makes changes to their products over time, and observations of earlier versions of products may not be fully representative of present models. (Viz., see measurements reported here a few years ago by "clinresga" comparing his VaH in one residence to a measurably quieter more conventional system in another residence.) kas