Here's the ducting, looks like a narrow feed to the current hood, but that shouldn't be difficult to change.

Sorry, by simplifying I meant messing with the cabinets and overall layout as little as possible. Cabinets will have handles changed and be refinished.
Will have high BTU burner outside for high effluent cooking. Found a Kobe hood that has specs I'm looking for. 2736sqb1: 720 CFM, 21" deep, 6" high, baffle filters. Adequate for 30" Miele Induction?

There are several manufacturers out there. I happen to like Kobe, but there are others.

Check the current rating (the breaker, perhaps) for your current cooktop in order to know what size induction you can handle without a wiring change.

I'm planning on having to update the electrical.

Also looked at many other ones, but it's difficult to find one with a decent amount of CFM that's in a low profile and has decent depth. Zephyr has some, but I'm concerned about their baffle less design, recommended way to clean is to spray grease cutter into the fan while on at low speed. Seems like baffles would be better.

"Adequate for 30" Miele Induction [without high effluent cooking]?"

Probably. The important criteria include (a) air velocity at the baffles with system in place with duct and MUA restrictions, (b) uprising effluent velocity in low effluent cooking conditions, and (c) sensitivity to odor escaping the capture and containment process. Effluent velocity is proportional to temperature of the food at the cooking surface, so if this is lower than frying or grilling, then I would expect a lower velocity and hence lower required air flow rate per square foot of hood aperture.

A 24 x 36 hood (six sq. ft) would normally want to have available 6 x 90 = 540 actual cfm (maybe 800 cfm rated), but without high temperature cooking less will do. This is not amenable to an simple calculation because the lower the uprising effluent velocity, the more susceptible the effluent plume is to cross drafts, and, I suspect, the wider the plume angular extent may be.

In other words, in the limit of just warming cilantro, the hood will likely be ventilating the room rather than capturing and containing the cilantro odor. (Who would mind, though?)

kas

Does the height of the hood itself (not the distance from the cooktop) have much influence? I picture it as a reservoir that has a certain capacity. Depending on airflow, (in and out), eventually it will fill up and start spilling out. That's why I asked about downsides to a low profile under counter system, I can't see how it could capture as well as say a pyramidal chimney. True, or am I over complicating this?

The shape above the baffles can affect the uniformity of flow over the baffles. Pressure losses occur due to shape transitions that aren't smooth. (A logarithmic horn would be ideal if one had an entire house story to put it in.) I think that there is a point, sometimes seen in particularly thin hoods, where good flow uniformity over all baffles will not be obtained. A height that is at least 20% of the longest dimension (if the duct is centrally located) will probably be ok, but I haven't seen any good analysis of that.

Baffle flow uniformity with a rectangular box will vary with air flow rate; only when the flow rate is at the high end of the design rate will baffle pressure loss force the flow to be more uniform across the hood aperture. Tapered hood guts tend to even this flow over the flow rate range. Commercial hoods are tapered upwards internally.

kas

I thought you might like to see my Kobe low-profile, undercabinet hood. I love the look and it works well, but it's a little loud for me.

BTW, the cooktop is a Bosch 30" induction

Thanks, does look nice. How many CFMs does that one pull?