Long time reader, first time poster. Thanks so much for all of the insightful discussions and everyone sharing their experiences with kitchen appliances etc. I have a question that seems like it would be easy to answer, but neither my cabinet people nor several range providers seem to be able to answer... I am setting up my range vent with a Fantech in-line blower (FKD8XL) and silencer. I know I need to get a "liner", but all of the pictures I have seen of these seem to be just the "insert" - filter, lights, rheostat, mounting into the hood. Now, the hood is a slant top, and I was expecting for best laminar flow, that the hood itself would be lined with SS or aluminum and that the insert would connect to that - i.e. that immediately above the liner the vented area would gradually get narrower as it goes up to the duct piping. Like a pyramid. But the pictures I see, such as this one: http://www.fantech.net/accessories5_02.jpg seem to show the duct connected immediately behind the insert. This seems like it would work great for just the center of the filter, but very poorly at the edges. Do hoods shaped in this manner exist? Or are they all just flat as a pancake immediately behind the insert? Finally, any recommendations for the insert? Seems like most would function exactly the same, and that one could shop for cost. The sound and power of the blower itself seems to be the main differentiator. (I've been thinking filters rather than baffles, but could be convinced) Any advise is appreciated! Brad

I am the resident expert only because real HVAC systems engineers don't frequent this forum, as far as I know. Noise introduced into the kitchen will be significantly reduced if an external blower with silencer can be fitted. A lot of the high frequency blade tip turbulence caused noise will be removed. This is also true of an in-line (duct mounted) blower. The issue of the neighbor is difficult to assess. What is the configuration of his or her windows relative to your potential external blower (1500 CFM I assume you meant). Your own window sound transmission is also an unknown. Generally, the external noise could be abated by (a) using a silencer on each side of a duct mounted in-line blower, or (b), using a deliberately under-driven* "up-blast" commercial blower (mounted as a side blast). (I think opaone is using an under-driven blower for his new system.) It is also possible to use a chase to move the blower up to roof level. I have a 1500 CFM nominal Wolf (Broan) blower on my roof. Its sound level is detectable but not obtrusive from the ground, but it might be if in a wall location where the sound is "trapped" between two houses. Possibly a more expensive but similar in design Abbaka downslope unit would be marginally quieter. ------ * commercial blowers of this type can use a pulley system between motor and fan that allows for different ratios. By choosing a ratio that operates the fan blades below their rated speed when the motor is receiving maximum voltage, significant turbulence noise can be avoided. The physical cost is a larger unit than would otherwise be required for the desired flow rate. Residential blower fans are directly coupled to their motors.

The wrapping will help with vibration carried down the duct sheet metal, but not so much with acoustic noise carried down the air path. The silencer has to be larger than the duct for the same reason that a car muffler has to be larger than its exhaust and tail pipes. The acoustic waves have to be partially delayed to mix with out-of-phase waves to cancel some of the sound, without adding significant pressure loss. An alternative to the silencer for reducing blade tip turbulence is to operate the blower at a lower speed. For the same flow rate, this requires a blower that is larger in diameter than the usual manufacturer matches to desired flow rates. (Compare and or contrast a Casablanca type ceiling fan -- many CFM with no noise.) For kitchen ventilation, I would look into a commercial up-blast blower. These often have a belt drive between the fan part and the motor, and the belt sheave ratios can be changed for various purposes. So a, say, 2200 CFM rated blower operated with a sheaf ratio such that at full power the flow rate is actually only 1200 CFM, or whatever you need, should be considerably quieter than say a Broan 1200 CFM unit operated at full power. There are many up-blast blowers available from commercial ventilation distributors, but determining what you need may be difficult. It would be for me without getting the necessary literature. You may find a source such as Greenheck to be willing to provide some advice over the telephone or someone at a local commercial HVAC outfit. It is also possible (I've never looked into this) that Fantech could provide some low speed in-line blowers that together moved enough air and could be set to be lower in speed. This might be asked of their engineering support via telephone. But I would be surprised if they could do so without exceeding your duct diameter and still interface to the duct without pressure loss issues. Anyway, usually roof installations are easier to access than duct installations when the duct is nestled in the joist space and covered by gypsum.

Thanks for help. FWIW, the distance from concrete soffit to floor is 7 feet as expected. I have narrowed it down to either Zephyr or Kobe insert liner as both have the horizontal vent in the rear. The horizontal attachment will be moved slightly to the left as that will be where the new cooktop will be moved. I am assuming that there will be some kind of attachment to the current opening which vents to the building's venting system - whence it goes after it leaves my kitchen I have no cares as long as it passes inspection. I am not familiar with either of these brands - does anyone have any recommendations as to one or the other. My venting needs frankly are minimal as I don't deep fry and will have an induction cooktop. I am considering mid range in each brand: KOBE CORE COLLECTION - This retails for about $850. It's ADA compliant with a remote which seems like it would be more convenient than reaching for controls under the cabinet. Monsoon I Insert Monsoon I takes one-piece liners to the next level. Includes dual-level halogen lights, and ADA-compliant wireless remote control, 6-speed electronic controls and either a powerful 600 CFM blower (30″ and 36″ models) or 1,200 CFM blower (42″ and 48″ models). ACT™ available on all models. Vertical and horizontal Zephyr - I couldn't find any functional difference in these two models except one has slightly higher CFM but I am sure the lower would be perfectly adequate for my needs DELUXE IN26 SQB-650-5A BUILT IN / INSERT 30" - 36" 700 CFM $803.49 PREMIUM IN2630SQB-700-2 BUILT IN / INSERT 30" - 30" 750 CFM Build.com $771