Kitchen Large Electric Appliances - duct for downdraft in a stovetop

I'm looking for information on the duct that has to be installed on the downdraft of a Jenn-Air stovetop. Believe it or not the installation instructions only say it needs to be installed. It does not say what type of duct, what size, or how long it can be. Can anyone answer these questions? We bought the stovetop from Sears, but they would not install it because it's new construction and not a replacement. My plumber and electrician does not want the responsiblity of installing my appliances. So that leaves me installing the duct to the downdraft.

Thank you
Dot

Dot: welcome to the forums! The downdraft, obviously, has to be vented downward through the base of your cabinet, through the floor and out a horizontal run to the outside of the house via a weather proof vent. Now, with that said, can you access the joisting under the floor where the stove is installed? You should use solid vent pipe, and not the flexible pipe, since there is a possibility of a grease accumulation in the pipe and the corrugated type holds more of it. The installation instructions for the stove top should indicate to you the size of exhaust pipe to use. Generally it is a 6", depending on the cfm of the fan itself.

I've got the hole in the foundation for the duct work, I just don't know how long the duct can be. The installation instructions say that I can't have anymore than 3 elbows, but don't give the length of the vent or duct work.

The elbows constitute a restriction zone, and that is why they are limited. Straight duct has no restriction so they don't limit its length.