Installation of a chimney on an exterior wall with 50 cm bricks

What is the benefit that you expect from the solution? Less dirt? The chimney sweep can come when no one is home ([holiday home])? We have no cleaning door in the exterior wall – given the thickness of today’s walls, I would have considered that a hardship for the chimney sweep. The boys’ wood-burning stoves lead into an internal, clad stainless steel chimney, and the masonry heater leads into an external stainless steel chimney.

According to the plan, it is intended to place the chimney directly adjacent to an exterior wall. Our first approach would have been to make the chimney accessible from the outside (through the 50 cm thick exterior wall). However, the master builder is far from enthusiastic about this idea (keyword: thermal bridge, cannot guarantee long-term tightness).

I am not enthusiastic about the whole detail: in all plans of the thread the chimney / flue penetrates the exterior wall – and a cleaning hatch would also pierce the ETICS. Who comes up with such nonsense, and what advantage is this supposed to have?