Change the layout. Downdrafts suck because they don't suck. Or get an overhead hood. But only if you have enough room to the sides and behind for this to be a safe set up. And most that you see are unsafe.

This is for an existing kitchen island. We have 18 foot vaulted ceilings so an overhead hood is not an option unless we relocated the cooktop. That would involve changing the floor plan and we aren't prepared for that. We rarely have the need for exhaust but I want one installed for the once a month occasion when opening windows and skylights isn't possible.