This microwave can support 3 different venting options.
1. Horizontal venting through the wall.
2. Vertical venting through a roof mounted vent duct
3. Recirculation venting into the house
The first two options require an existing vent duct work (or you gave to have one installed. The third option does not require any duct work, however this option is not recommended for a gas range as it will not vent the carbon dioxide outside of the house.