If you have a couple of bends and if you can't fit a large-diameter (i.e. 10") round duct between the floor joists, you won't be getting anywhere even close to the full CFM. Your downdraft might do much worse than you'd think.

I also have my doubts that even with a perfect duct, the small opening on a downdraft would be able to admit even close to 1500 CFM.

On the other hand, if you are OK with all the known problems with downdrafts, then the Best is generally considered one of the better choices. On the other hand, the Dacor looks as if doesn't extend even anywhere sufficiently high to being effective; and it also appears to have mesh filters that are particularly hard to keep clean. You'll almost certainly lose a lot of air flow in those filters once they get even minimally dirty.

Is there any way you can make the duct shorter, have a bigger diameter, and get it straight? Otherwise, please reconsider and get an overhead hood, which is likely going to perform much better anyway.

We have too tall of a ceiling so will be going with downdraft.

M wrote, quite rightly: "I also have my doubts that even with a perfect duct, the small opening on a downdraft would be able to admit even close to 1500 CFM."

I have a 1500 CFM Wolf blower (made by Broan) pulling air through a hood entry aperture of about 10 square feet, (with 50% baffle blockage) and the estimated flow rate given the duct and particularly the baffles is around 900 CFM assuming nearly perfect MUA. A 1500 CFM (at zero static pressure) blower on the unit I saw illustrated looks to me like a poster child for choked flow.

Even if the entire panel facing the cooktop were open, the slot below it is only about a half a square foot in area. So I have some doubts about the data sheet's blower compatibility list -- at least at the 36-inch unit level. A pressure loss of 2 inches w.c. would cut the flow to 200 CFM on the EB15 remote blower. There might be a better blower having a lower zero static pressure rated flow rate but higher cut-off pressure that might overall, in situ, yield a better flow rate.

The real issue with these side-draft schemes is that they cannot develop enough air velocity at any distance to pull hot cooking plume effluent sideways into the collection gap. The plume from simmering bacon on a back burner has a chance of being collected, as would poached fish odor (also a low velocity plume). Plumes from wok cooking on a front burner seem to me to be an impossible task to capture this way, as would any grilling or searing (plume velocity at least 2 ft/s on induction, heading upward).

Plumes starting at a pan expand in diameter about 4 inches per foot of rise (10 deg half-angle cone). So ceiling systems need to be quite large to have good capture, and that is without any transverse plume disturbing drafts. Commensurate air flows are needed for the exhaust and make-up air.

For economic reasons, commercial hood systems are the most effective at capture and containment. Every deviation from their design for the purpose of aesthetics has a price in degraded performance.

Assuming you have 12" floor joists, you aren't going to cut a 10" hole in them.

its a new build - so the builder will do whatever is needed and not cut corners - I will ask to make sure He’s not doing holes in the joists

it has to be a downdraft so I have to make a choice. I picked Dacor (because I have it in my current home). He suggested Best - so posed the question because I dont quite Know how they compare. @M and @kaseki - you seem to know a lot of what is involved (most went over my head!) I have reread the comments!!!

No, you don’t “have” to get grease all over your cabinets, and smells in your soft furnishings, and a loud ineffective downdraft. You most certainly can do an overhead vent in an appropriately designed kitchen. If you can’t, the kitchen is inappropriately designed and isn’t considering needed functionality.

Questions about venting come up quite frequently in this forum. The discussion usually covers one of the following topics:

1. Recirculating hoods are noisy but have almost no effect other than possibly redirecting hot air away from the user. And even that job is too difficult for many models (e.g. over the range microwaves)

2. Downdrafts are almost equally inefficient. If everything else fails, then a downdraft can be a compromise solution when using induction, having make up air, and restricting yourself to the back burners. Don't expect miracles though. This is only barely better than no vent at all. If you cook no smelly foods and only at low heat, you might not mind. Otherwise, reset your expectations.

3. Rated flowrates for fans are almost never reached. You need large round ducts, few turns, a good make up air system to add fresh air that replaces the vented air, and a large aperture at the hood. And then, maybe you'll achieve about 70% of nominal.

4. Don't put the stove into the island. It is exceptionally difficult to design a functional kitchen around that.

There are a few more topics, but this is generally it. And while the question comes up often, home owners not only keep asking the same things, they also frequently get very upset when they hear information that they don't like.

Everybody in this thread of course knows and has been trying to break the news gently. We don't want to be the messenger who gets shot. But the gist is that your design has several red flags and will likely leave you with a venting solution that doesn't do much good. We know how to fix this, but you won't like that it involves major changes.

So, everybody just tippy toes around the problem and gently prods you to make at least incremental changes