The duct work is already installed on the microwave right out the box, and cannot be removed for built-in installation. It is needed to vent the microwave for fire safety. The microwave sits just over 12" inches tall if all the duct work that comes built-on is removed. It's not possible to remove only the top and lower the height of the microwave. The measurements of the trim-kit sash (not to be confused with the duct work on the mwo) are below. Measured to the nearest 16th of an inch. Click to enlarge photo.