Simplest solution if you're getting a MA hood. Call them. Ask to speak to Jeff Herman. He will walk you through the process in a clear and helpful fashion. That is infinitely easier than trying to start from scratch. Once you've done that, post back here with specific questions and you'll get all kinds of esoteric answers.

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

TonySak, thank you, I didn't know the cleaning would be easier. Since we can do an external blower, that's a plus in that direction. I think that is one we are looking at right now, the Broan Elite 619004EX. The other option is one by Best, model KEX4236SS. There's a big difference in price, so I'm trying to figure out if it is worth it. Links in case anyone is interested: http://www.ajmadison.com/cgi-bin/ajmadison/619004EX.html#BVRRWidgetID http://www.ajmadison.com/cgi-bin/ajmadison/KEX4236SS.html

Deeageaux, you just totally burst my bubble. The past three days I've been narrowing down my rangehood selection and I was feeling really good about the Kobe under cabinet CH-191SQB-1. Powerful, quiet, newer LED lighting, looks are ok although wife prefers a more classic pro-canopy look versus the sleeker slightly more modern look of that particular Kobe. Then I read you post above regarding depth. I quickly check and lo and behold, every Kobe ( I looked at 6-7 models, every under cabinet and even several wall mounts that can be under cabinet as well) is only 22" depth. Is this a deal breaker? It seems like a critical thing to me as the most powerful and frequently used burners are on the front. My cooktop with be a 36" 6 burner rangetop, brand not 100% decided but likely Bluestar. I'll have to go back to the drawing board on this selection I guess.