90mm Kneepipe 90 Degree
This right-angled bend is necessary in any case for a stove with a rear exit. For example, when you want a cooking plate on top of the stove.
It can also be used to guide the flue, but this will negatively influence the draught in the chimney. Preferably use a gradual transition with a 45-degree bend or compensate the lesser draught with an extra piece of pipe (insulated) outside.