Rereading this thread in its entirety -- a trip down memory lane -- reminded me of some web sites with filters on their search function such that when one clicks on enough constraints there are no candidates left to purchase. feisty68's constraints have a similar effect. Thinking that maybe there is some way out of the box, two concepts come to mind to bring up: (a) One can choose a hood with internal blowers (as seemingly required) that has more specified flow than the external duct can handle. In this case, at full power the flow will be low, (or possibly zero, depending on the fan curve shape), but when run at part power to yield an appropriate flow rate for the duct, there should be reasonable flow. Whether this is adequate flow would require some analysis. At partial power the blade tip speed will be less and lower noise should result. For example, a VaH hood with two motor squirrel cage fan assemblies run at part power would likely still expel grease onto their housings as intended. Choked flow, however, may be sooner (CFM-wise) than a similar over-sized conventional blower / baffle system due to the nature of a squirrel-cage blower (as implied by VaH CFM vs. pressure loss data). I wouldn't want to guess which approach was louder at the power setting that was at the point of diminishing returns, CFM-wise. Related to this category is using an inline axial blower designed for higher pressure loss at the desired actual flow rate. Fantech might help here. Such blowers may be noisier, so an in-line silencer on the hood side of the blower might be essential. There are screaming-mimi aerospace fans that can push 1600 CFM through a six-inch duct. (b) The other concept is a hybrid exterior/recirculating hood scheme. I think both Best and VaH have examples of recirculating hoods. In this concept, if the actual systems are so configurable, the path to the filter pack would be split with one branch going outside. When the pressure losses of the exterior duct path rose high enough as blower power increased during heavy cooking, additional flow would be through the filter pack and back into the room. Some recirculating hood users here have commented on effectiveness and noise and their threads might be discovered and checked for relevance. Obviously, the simpler approach here is recirculating without engaging the external ducting. In that case, a separate soffit blower, soffit face register scheme could be used for further kitchen overall ventilation, helpful (slowly) when the oven is opened. kas

I've been very pleased with Vent-A-Hood. It works extremely well and is as quiet as you'll find, unless you go with a remote blower of some sort. That being said, we planned for an optimal installation. The ducting goes straight up through the attic (less than ten feet). No turns, and terminates in a properly-sized roof jack per Vent-A-Hood specifications. My current system was installed in 2005. I think that that in quite a few cases, the source of dissatisfaction by some owners has more to do with complicated installations, involving several turns in the ducting, long duct runs, or constriction at the roof jack. I cannot over-emphasize the importance of a proper roof jack. The system in my kitchen operates flawlessly and is very quiet. Even when turned on full speed, it doesn't interfere with conversation or require the television to be turned up to a higher than normal volume. Most of the time, I run at the very lowest Sensasource speed setting. Even then, nothing escapes it. I know this because I have recessed can lights throughout the kitchen, and if I had smoke or air-borne grease flying around, I'd be able to see it in the beams of downward light from the cans. As for your installation, I think that if you can forego cupboards above the hood, it would probably make more sense to go with one of the wall-mounted or chimney-style hoods. Matching shrouding is available to hide ducting on the wall-mount models. Look for a model that can be ordered in 27" depth. You'll need the extra depth over a commercial style range. Far more important than a strong blower is a large capture area. Having a range hood that extends beyond the the perimeter of the cooktop will allow you to capture more with the blower running at a lower speed. You should definitely try to install a hood at least 6" wider (3" on each side) than your cooktop, and one that extends out to the front of the burner area, If you have room to go with an even wider hood, that's even better. My range hood is 12" wider than the cooktop and extends out to the cooktop leading edge. Other manufacturers make hoods in similar dimensions, but I like Vent-A-Hood and recommend it. I've been entirely pleased. The important thing is capture area. The larger the hood, the more you'll capture, and the fewer cfm's required. Keep in mind, if you air condition in the summer and heat during the winter, all that air you're exhausting you've paid to cool or heat. You might find interesting the Vent-A-Hood video that the link below will take you to. Granted, it a piece of Vent-A-Hood marketing hype....but it does contain some useful information. Here is a link that might be useful: Vent-A-Hood video

Consumer hoods are much louder than commercial hoods, primarily because consumer hoods have a small aperture (bottom opening) and no containment area so they try, unsuccesfully, to make up for this with higher air flow rates. More: https://www.gardenweb.com/discussions/5161173/hood-faq It's always surprised me that I can stand by a commercial hood pulling 1400 CFM and eliminating nearly all effluent, odors and grease and carry on a quiet conversation while consumer hoods, whether 300 cfm or 600 or 1200 are massively louder and much less effective at removing effluent, grease and odors. The best way to reduce noise is to get a commercial hood from someone like CaptiveAire. These are really not that expensive but are larger which some people don't like. Otherwise, you should use an inline or exterior blower (e.g., no blower in the hood itself) and install a silencer between the hood and blower.

It would be best to start any quest involving kitchen ventilation to study the literature, or at least study the many many threads here on the topic. I would prefer to write answers to questions that are based on my possibly inadequate previous writing than generate yet another long message covering the entire topic. You may wish to start with the "Hood FAQ" which can be found by searching. I believe it is listed under @opaone. Hoods are about capture and containment, and success in this depends on many factors, the most critical of which is sufficient air flow velocity at the hood entry to ensure that which is captured is contained and expelled from the residence. This velocity is independent of how many burners are running at once, but rather what the cooking surface temperature is plus plume heat augmentation by gas burners. In any case, the 100 CFM per 1000 BTUh is derived from certain standardized commercial hoods, not residential hoods. See the Greenheck Guide available at https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf for comparison between the 100 CFM per rule of thumb and the hood aperture velocity rule. I suggest 90 CFM per square foot of hood entry aperture, and this aperture needs to be large enough to overlap the rising and expanding cooking plumes. Let me adjust the salesman's statement: "...because the design pulls more air than a filtered/baffled hood of the same [zero static pressure rated] cfm [when hanging unattached to anything in free air]." Ventahood use squirrel-cage blowers that also perform the function of baffle filters, thereby eliminating that cause of pressure loss. However, as blowers go, they are more susceptible to other pressure losses than conventional blowers, and hence if there is extensive ducting, or inadequate MUA, their flow rate will be less than the actual rate asserted. My guess is that you should have a 24 x 42 inch hood aperture, requiring an actual 630 CFM obtained from a 900 - 1000 CFM rated blower. Read MUA related threads to determine how closely the interior air pressure has to match the exterior air pressure for safety. Your state may require heated MUA. There are a lot of ways to accomplish MUA under these conditions, and the threads here should help you understand what you have to tell us to allow better tailored help. kas