Unfortunately we haven't gotten that far yet. :( It's still sitting in the garage. I'm expecting it to happen in July. I am sure it will be fine. The fan unit is quite big, so we're thinking anything that size has got to be great :)

Sailormann: Are you putting a 10" duct for that? I thought that was what I read but my husband said that sounded huge.
The vent that it hooks up to at the downdraft is 10 1/4" x 3" so it seems like that 30" surface area would be the limiting factor in the system, but what do I know? We'll have about a 25' total run and one 90 degree elbow.

I'm not even sure we could do it because the place where the duct runs is like grand central station for HVAC, plumbing and central vac. While we were checking the current ducting we noticed that it is only 7" across when the installation instructions say 8". That means the size increase will be even more than I thought. Reading the old installation instructions we also discovered that the venting could have gone straight down out the bottom like the units do now. When we built our house, the dingleberries that installed our downdraft had the vent come out the front of the downdraft unit then put in a 90 degree elbow to go below the floor and another 90 elbow to take it horizontal to the exterior. It basically took up the entire cabinet.