Hi there, an upright Dometic 3 Way Fridge requires correct installation and ventilation to ensure optimum performance and safe operation. You can see listed on the product page under the Accessory List there are Vents and Gas Flue kits required as part of the installation. On the INSTALLATION GUIDE  document, you can see what recommended vents and gas flues go with your particular sized fridge.
For customers buying a Dometic fridge to replace their existing one, they often already have the required installation accessories (vents and flues) and may not need to add them to their fridge purchase. Thanks.