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 :)

What you won't be missing after a while is the grease that will accumulate in the device that takes heat or cold (physicists need not point out the sloppiness of that phrasing) from the outgoing air and puts it back into the incoming air. Any effective and practical heat transfer device that I can think of will collect grease and dust in this application. I don't know how easy it would be to clean such a unit, but my guess is that they are not designed for this. Essentially, all kitchen ventilation puts effluent into the environment. This is nearly inevitable. The only question is what kind. Residential units and most commercial units pull grease, smoke, and water vapor from the kitchen and put it directly into the environment. The probably rare UV systems convert the effluent to simple molecules, but then the ozone they generate has to be vented, or somehow filtered out, perhaps by charcoal, generation of which has its own issues. So the only thing green about a kitchen is the paint, and the goal is to minimally risk fire while getting rid of the effluent. However, my view on this is somewhat speculative. A commercial HVAC company that deals in large HRV might have something that would be practical. Perhaps some need for commercial heat recovery has spawned a practical kitchen venting HRV. The Fantech has a washable filter. How long would it take for cooking grease to gag it? What of potential grease fires. And the specified cfm has to be reduced by all the other pressure losses, so you would likely need a larger unit anyway. kas

There are a few sources of noise in a hood ventilation system (and potentially also in a powered make-up air system). The dominant noise when a silencer isn't or can't be used is fan blade tip turbulence noise. Second will be either baffle turbulence noise (more like a hiss), or its counterpart if mesh filtering is used, or duct turbulence noise. Baffle noise domination assumes that the duct is damped on the outside and the air velocity in the duct is not too high. Otherwise duct turbulence noise may dominate baffle noise, and the duct may also rattle passing on blower unbalance vibration noises. External blower noise is usually lower with a long duct than with a short duct, but one should not expect a really big reduction in noise just because the blower is outside instead of in the hood (for equal volumetric flow rate). (The exception would be a commercial external blower, configured deliberately so that the fan is oversized and the belt drive sheaf ratio is set for a slower tip speed.) For residential operation, where room for a silencer is available, an external roof blower and inline silencer is the quieter approach, leaving baffle hiss below normal speaking levels at full power. That is my configuration. Part of the duct turbulence noise will also be removed -- that from the duct between the silencer and the external blower. Fantech silencers are larger than the ducts, e.g., 14 inches in diameter for a 10-inch duct. http://www.fantech.net/products/fans--accessories/accessories-ventilation/silencers/ld/ld-10-silencer/ They have the general appearance of a motorcycle muffler scaled to a dragline excavator engine. The silencers are also somewhat longish, so if the duct was going to go up into an attic and straight to the roof at the roof edge, it would be necessary to use an angle duct after entering the attic to extend the duct length in the attic to accommodate the silencer, thence use another angle to bring the duct to the roof. Avoid horizontal ducting if possible. Try to make the ducting accessible if possible.

With conventional hood systems, the expectation is that the larger particles within the entire grease particle spectrum are collected by the baffles, and the smaller particles are ejected into the outside air, with only modest condensation or impact collection by the duct. To deal with the entire particle spectrum with a filter pack is a challenge, and probably unaffordable in cost for most residential users. If the Amazon rating is based on comparison to outside venting, the result above might be reasonable. As a commercial example, the Wells WVU-31CT filter system is described below: "Filtration Completely self-contained filtration process reduces emissions below that allowed in NFPA 96 and ANSI UL710B using the EPA 202 test method and includes stainless steel grease baffle filter with grease cup, fiberglass pre-filters, high-efficiency (Particulate Air) filter/ carbon-charcoal filter pack. All filters are easily removable with out tools. Air flow sensors continually monitor air flow optimizing performance and grease removal while an interlock system will not allow cooking appliances to function if filters are missing, clogged or in the event of a fire." About $18k. Electric surfaces only.