Wealthy homeowners have been known to discuss this. Gardenweb started out for gardeners, years ago, and built forums for the homeowner side of things. Been going many years.
The tools are not as good as here. How to search one specific forum is not obvious at first.
68 threads on grilling in the Appliances forum.
8 on grilling+downdraft
One about dysfunctional JA downdraft. Search on "disfunctional" if this thread's URL is cut when displayed above.
- Other manufacturers say that grilling makes the most fumes possible so you need to oversize your vent motor for this.
- Other manufacturers say not to try downdrafting grilling fumes.
- In other threads in other forums it says not to downdraft for optimum performance.