The new flue system is easy to install with push-fit connections and a telescopic system which, in most cases, eliminates the need to cut the flue to size. This Vaillant black terminal kit provides a more aesthetically pleasing finish in black to the white one that comes with the horizontal flue. A terminal kit for a horizontal flue is the end of the flue that sits on the wall on the outside of the building and allows the flue gases to exit the building.