Keep looking!! I think there are great options out there still. If you need a roof mounted exterior blower, how about the Abbaka HyEx10 external blower? It's a very pretty, extremely low profile unit which according to the website appears to use 8'' duct and is rated at 1000 cfm. We almost went with the 1400 model until my contractor nixed it, as he was unwilling to go out onto our very steep roof to mount it. I also find the Zephyr rep's comment to be nonsensical. If you used a blower with a 10'' duct collar, you would mount the transition ducting right at the blower. Since it's mounted on your roof, any turbulence noise generated would be on your roof, not in your kitchen. It is true that pulling a very high volume of air into an 8'' duct will create more airflow noise at the point where your ductwork enters the hood, but that will be true no matter whether you use a transition or not, for a given cfm flow rate. So, in my mind, using transition should not really worsen the situation. Maybe another of the ventilation folks out there can see another reason not to use transition but I'm not convinced. Still, I think the best solution is to find a high flow blower that uses 8'' duct. I'd contact Abbaka. Here is a link that might be useful: Abbaka external blower

The big recommendation is to get a handle on the terminology. Exhaust is the function you want done. Cooking produces rising warm (steam, grease, smoke) air. Hood is an upside-down sink or umbrella shape that the bad air rises into. The industry often mixes terms up, and it actually doesn't hurt sales. So they may say "Hood" when they mean a whole lot more. Canopy, as a term, works because it focuses attention on the Hood alone. Capture Area is another word for almost the same thing. Make-Up Air, MUA, is the air that comes into your kitchen when you blow bad air outside. It is a lot of air. It replaces the volume of air you sent outside. In cold climates it has to be planned for as part of the house system. Windows are often closed. Duct is the conduit / pipe / tube or rectangular shape channel that your bad air travels down. Liner is almost the same thing. It actually IS a liner if it matches a special shape of hood... but once again, the industry will use this term "liner" to mean anything that creates confusion. Duct is made of smooth metal, not corrugated. Never made of plastic (this is Kitchen Exhaust) Filter is the grease catch that you want to have at the front end. Filter could be Mesh. Filter could be Baffle. Filter can only be that, in outdoor exhaust situations. Charcoal is not an option here. Blower is the motor that grabs that air and blows it outdoors. Blower can have spinning propeller blades. Blower can be squirrel cage. Insert is a combination of a few things, built as a package that you insert into a hoof and liner. Insert is a package of blower, filter, switches, lights, etc. The industry often mixes terms up, and it actually doesn't hurt sales since they get to sell their all-in-one products. They don't push inserts. Inline describes a blower located at some point in the Duct. Inline is not at the duct beginning (front end), and not at the Duct termination. Remote describes a blower located in a place far away from the kitchen. It can be at the end of the Duct, pulling (sucking) air instead of pushing it down the Duct. The industry likes to sell more than just a blower. A whole kit. An all-in-one solution. Something that parts fools from money. Consumers who know enough can separate all the variables. The industry does not promote inline blowers. Having an inline blower allows the consumer to buy the other parts as separate items. The industry does not promote remote blowers. Some are promoted as part of a whole kit. They can be bought separately. Blowers that are not positioned at the front end of the duct are not in your face. Noise is caused by several factors. The blower being in your face is one factor. Review: The industry mixes terms up. They will call anything a Hood. Exhaust is the big general term. "Will this Exhaust my kitchen air?" hth

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).

48 x 19 inches is a nominal 6.3 sq. ft. For good containment of what is captured (only the parts of any plumes that rise into that opening), you should strive for 90 ft/m = 90 CFM/sq. ft. or around 570 CFM. This calls for a blower rated at 900 CFM (check), but, the factor of 1.5 i used assumes that most of the pressure loss seen by the blower is in the hood baffles, and not the ducting and whatever passes for a make-up air system. (I forgot to ask about how MUA is provided; please do tell -- no air leaves the kitchen that isn't replaced via some path, and this path needs to be low pressure loss.) An actual flow of 570 CFM in a 6-inch duct (0.2 sq. ft.) requires a velocity of 2900 ft/min. Not likely to be achieved with kitchen ventilation blower designs and if it were achieved it would be pretty noisy and well above the recommended maximum of 2000 ft/min to keep down impingement grease collection. (1000 ft/min is the lower bound to minimize condensation grease collection.) While it is possible to add a booster fan with unpredictable interaction between blowers, better is to upgrade the duct size; 8 inches is a good suggestion. Replacing the exterior blower with one that can deal with significant pressure loss including that from the existing 6-inch duct is possible, at the cost of significant noise and perhaps expense, as the blower designs good for this purpose tend to be more like axial aerospace designs with tight clearances between blade tips and walls, and somewhat banshee like acoustics. Comments on the MUA approach will have to wait until we have a description.