How large is the duct, how is it routed (straight out the back, up and 90 degree bend, etc), and how far is it from the hood to the Abbaka? A silencer will be about 3 feet long, and about 4 inches larger in diameter than your duct. It should make a significant, if not tremendous, difference in sound level. Maybe something is loose and rubbing the squirrel cage in the blower, or some other mechanical failure. That might be evident if the cover can be removed for inspection. I see on their web site that Abbaka has a 7 year warranty, in case that helps. As far as more insulation, search gardenweb for "dynamat", which is a thin ( about 1/15th inch) rubber/metal foil product, most often used inside car door panels and trunks to decrease road noise and fix rattles, but can also be wrapped around your duct. I don't think you need that much coverage to dampen out some of the tinny vibration transmission, if that is what you have. It is rather pricey, at about $5/sq ft. This post was edited by attofarad on Thu, Jan 3, 13 at 22:30

Whether a 10-inch MUA duct will help will depend on the restrictions getting the air into the rooms of the house. For example, what sizes are the furnace to room ducts? Is there a furnace filter in place? Is the MUA flow going against the flow that the furnace and/or air conditioning move the air in the relevant ducts. Perhaps you could have a 10-inch duct to a Broan or other MUA powered damper that dumps into the house in some way before the duct continues toward connecting to the furnace. The damper opens when the flow in the hood duct is high enough. Generally, not liking cooking odors in high concentration or grease on the walls, I will always vote for more hood ventilation flow rate, within the bounds of good enough. Good enough for full containment (very approximately and very condensed) is a blower zero static pressure rated flow rate equal to the hood aperture area (sq. ft.) x 90 ft/min* x (3/2) for pressure losses. This assumes not too much restriction on the necessary MUA flow. Full capture requires the hood significantly overlap the hot surfaces from which grease and smoke effluent is being generated. Lower flow rates may be fine if only frying eggs and not bacon. Time searching this forum on MUA will provide more information and insight. kas ------ * 90 ft/s comes from the rising effluent velocity of 3 ft/s for hot cooking surfaces per references in my My Clippings, 60 seconds per minute, and an advantage of 2 for the flow dynamics of baffle hoods of nominal configuration (somewhere between a guess and an observation).

3ilovepie, you said your dinning and kitchen are in the same room. What does it mean? Do you refer to literally both in a room or just open concept? I had my VAH at full 900 CFM this evening, pan frying fish sounds louder than the hood. Have you actually listened to VAH's sound? In case of not, you can go to Caplan's to try it. They should have a live 2-blower model at the time I bought mine. 3-blower one sounds same or even slightly quieter than the 2-blower. IMO, cleaning is not really an issue. I don't even need a dishwasher to clean the dripping trays once a while.

All of the above may be true, but are not in themselves totally limiting. In general, there is always a blower that will move a desired air flow volumetric rate through a given duct, but one might not want to operate it, listen to it, or pay for it. But in this case we are on the margin, and feasibility is not prohibited using conventional devices. For example, I have a Wolf/Broan 1500 CFM rated roof-mounted blower operating with a 10-inch duct, and given various estimated pressure losses, expect that it moves 900 - 1000 CFM. A 1000 CFM rated typical hood blower, no matter how large the duct, at a minimum will be significantly restricted by the hood baffles, and at a maximum by any added MUA pressure losses, and would be unlikely to move more than 700 CFM in use with a hood. An 8-inch duct has a sectional area of 64% of that of a 10-inch duct, so the pressure losses operating at 67% through an 8-inch duct of the air flow rate through a 10-inch duct will be similar. In general, one wants to select a blower having a fan curve that supports the desired flow rate at the pressure loss that one estimates is present. Without my looking up the specified hood, let us assume that its entrance aperture is 42 x 27 inches or just under 8 sq. ft. This calls for 8 x 90 CFM/sq. ft. or 720 actual CFM. A typical 1000 CFM blower may achieve this with a 8-inch duct, and one certainly can check the assumptions against blower fan curves (where available) to either ensure adequacy, or at least force the MUA system to be active and not cause significant pressure loss. Note that this doesn't violate your appliance guy's opinion about duct flow rates, although I am sure that his view is based on typical in-hood blowers. If you have the room in some part of the duct path, then including a silencer will help reduce noise back at the hood for only a small added pressure loss. In any case, numerous commercial kitchen ventilation blowers can be found that will pull 720 CFM against any pressure loss likely from a well designed hood/MUA setup. It is quieter to move a given flow rate when the fan blades are large and moving slowly than small and moving quickly, as the latter generates more high frequency noise from turbulence. Induction motors can be controlled by rheostat adjusted phase circuits, and these can be put into hoods. My Wolf hood has such a control, and now the technology allows for it to be performed with better techniques at low cost. These comments are meant to touch on most of your questions, but feel free to delve deeper as needed. kas