With the blower on the roof, the closer the silencer is to the hood the more duct turbulence noise will be reduced, along with the blower noise (mainly from blade tip turbulence; motor rumble and other low frequency vibration will not be affected by such as Fantech silencers).

Is there a particular reason that the hood duct diameter and blower interface diameter are mis-matched?

What is the rated flow rate of the blower? What is the size of the hood?

In general, the duct size should be such that the velocity in the duct at full power (and considering that the rated blower flow rate is not the actual flow rate) falls between 1000 and 2000 ft/min, with the lower value less noisy. This implies that the answer to where the duct changes from 8 inches to 10 inches depends on the answers to my questions above.

I’m not sure why they’re mismatched. The hood is the Zephyr Vista Island 36” which has an 8” duct. It says it’s compatible with the Zephyr external blower, of which there is only one model CBE-1000 and it has a 10” duct. I just took a look at the In-line blower option listed for this hood (blower model PBN-1000A) and it’s also 10”. Both of those blowers are 1000cfm.

Pulled up the spec sheet. Looks like this is by design for some reason.

It would seem that the 8-inch diameter is what the chimney cover is intended to fit. Maybe it looks better that way. It also seems that they want the transition to be near the hood (above the ceiling).

My impression from the table notes above and an image I got from a search is that this is a non-conventional hood, i.e., not baffled and lacking a capture volume reservoir. Generally, the farther a hood deviates from commercial design, the less efficient it will be in capture and containment. It looks like it has mesh filters. While a 1000 CFM (in free air) blower might move 650 CFM through a conventional baffled hood, I can hardly imagine it pulling that much past a mesh area. And this mesh area does not appear to overlap the cooking zone.

Recommend review of myriad hood threads here to gain perspective about hood design principles and requirements. Note that in many municipalities, a 1000 CFM rated blower will require a make-up air (MUA) system. You may wish to review MUA-related threads also.

I looked through many many hood models and wasn’t able to find any that were baffled, other than commercial models that would not have fit our space and low ceiling. I chose this one as it was the highest cfm available for a low profile which I assume will make up for at least some of the issues with mesh and lack of capture area. It at least beats an equivalent style hood with only 600cfm

True, but only if the mesh area does not choke the 1000 CFM blower to be barely better than a 600 CFM blower. This will depend on their relative fan curves.

I am only here to aid in achieving the performance that is desirable from hood systems over the full spectrum of potential cooking activities. You are welcome to let aesthetics dominate your trade space.

Most 'pro-style' hoods have baffles. Although the Wolf Design guide lacks imagery of the guts of their hoods, I think most of the higher flow ones have baffles.

My Wolf hood is shown below. It hangs from an 8-ft ceiling via a 6-inch extension. While much longer than you need, and an island hood as well, it illustrates what can be done in an 18-inch height hood. Modernaire, Prestige, Abbaka, and many others surely have baffled hoods with some volume below the baffles that can be fitted to your architecture.

If your ceiling is only 7 feet high, then a lower profile hood may be desirable if you want the hood base above 30 inches. Baffles with some slope should still be possible.