How to Attach a Vent to a Microwave Damper

Mount the microwave under the cabinet as instructed by the manufacturer. Note that this also requires cutting a hole in the bottom of the cabinet to accommodate the damper if you are installing a microwave for the first time.

Look into the bottom of the cabinet hole to locate the damper, which looks like metal or plastic flaps. Remove any tape that holds them in place, and discard it. Gently move the damper blades up and down to ensure that they flow smoothly without obstruction.

Locate the raised metal box, which is the damper plate, and place it over the cabinet hole until it is centered over the hole in the underlying microwave damper. Insert the provided screws into the holes on the damper plate, and tighten them into the cabinet, using a screwdriver.

Push a 3-inch-high vent extension piece down over the damper plate, and secure it, using duct tape around the bottom edge.

Insert a rectangular-to-round duct transition piece on top of the vent extension, and secure it along the bottom with duct tape, as well.

Pull the rigid metal duct that extends from the wall down until it slides over the rectangular-to-round transition piece. If the rigid duct is too long, put on work gloves, and cut it down to size, using tin snips. Wrap more duct tape around the bottom edge of the round duct to secure it.

Proceed with installing the remainder of the external microwave vent, including the external vent cap