Product review (3 stars): It's nice they don't tell you that on the box
You will need 3 1/4" x 10" rectangle to a 6" round duct transition for installation. It's nice they don't tell you that on the box, but you find out when you're in the middle of the install and it tell you on step 14 that you need that piece. Also, the unit I installed had absolutely zero hardware, so yet another trip to the hardware store for the screws to hold the plenum onto the bottom.of the cook top and the nuts holding the fan to the plenum