Complete joke.

In what way?

It’s a giant marketing whopper to even suggest that it can do 1/100th of what an overhead vent can do. Surface mounted downdrafts are giant scientific jokes, sold to people who never cook, and have no expectations of actually venting. Because it won’t do anything real. It can’t. Science says so. Despite the marketing spinners.

@User: While you are correct, in my view, that this device is over rated, misusing the term 'science' in the same manner as, e.g., climate modelers who can get any result they want from simulation, or other recent examples in other fields, is not the best way to be persuasive, particularly to anyone who actually knows what science is and isn't. Better to use observational data and supporting theory to estimate behavior.

Cooking plumes have been measured and reported (1) and behavior of air flow into apertures published (2). Approximate performance of particular cases can be extrapolated, but only qualitatively. Computational fluid dynamics can be more exact, but even there the modeling needs to be very carefully performed.

So my point is to not invoke 'science' as a standard because those who are aware of the term's egregious misuse will not consider it a valid argument by itself.

______

(1) Thermal plumes of kitchen appliances: Cooking mode, Risto Kosonen, Hannu Koskela, Pekka Saarinen, Energy and Buildings

(2) HVAC Applications, 2003 ASHRAE Handbook, Chapter 30

You would be better off installing your cooktop on a wall where you will be able to install a ventilation duct to the outside, and have a nice overhead hood. You will never be happy with what you've proposed in your OP, and you will be cooking there for years, and be unhappy with it the whole time.

@M Miller wish it was that easy. Am in an apartment, smallish kitchen, the hob is currently against a wall which will be removed to create the island. Current rangehood is ducted into the ceiling cavity. I know, I know … terrible.

@User thanks for explaining. Am in a bind with it as eternal ducting not allowed in my building. Appreciate your reply.

@kaseki I am currently remodelling my kitchen/diner and plan to have a hob positioned in a peninsula. I have been looking into ceiling extractors but concerned due to the height, they may not be efficient. I have come across the integrated vent hobs, but very interested in your comments regarding the efficacy of these units. In your opinion, would you consider a ceiling mounted extractor better than a downdraft, even with the ceiling height taken into consideration? Our ceilings are around 2.3m. Thank you in advance.

@Louise Blay: You left out too many parameters to make a decisive argument either way. Let me explain. The down-draft, or pop-up side draft that pulls effluent sideways and then downwards, can be effective against very low velocity grease entrained plumes such as might be generated by low temperature cooking, bacon simmering (but only if proximate to the pop-up) and perhaps fish poaching. I believe I argued above and in other threads what the plume diversion issue is between the possible air flow into a slot and the upward momentum of a hot oil/grease cooking plume.

On the other hand, a flush ceiling register that is smaller than the plumes that make it to the ceiling will not capture moist greasy plumes impinging on the ceiling outside the register area. Slotted versions may pull air along the ceiling, but this won't be fully effective against impingement or thermal condensation of moisture and grease particles. You want overlap and whatever amount of below baffle reservoir is feasible.

There is an intermediate case you don't exclude, particularly by your use of "ceiling mounted." A hood mounted into the ceiling that has a base at 7 ft (2.1m) or even lower depending on chef head contact can be effective if the hood entry area is at least 8, better 10, inches (20 - 25 cm) larger than the boundary of possible pan edges on the cooktop. What are the joist cavity dimensions in your ceiling? Even with a flat ceiling scheme you need to use the joist cavity for installation.

Please provide some insight into what you cook, tolerance for grease and odor, and how fanatical you might be with respect to hood visibility.