We could now spend pages discussing what an architect "must" be able to do (liberal profession, cf. doctor), which law regulates what for the chimney (or not, cf. district chimney sweep master) and what does not fall under their responsibility.
I just did some research on Google. This research brought me to the following knowledge within 5 minutes:
1) The person responsible and accountable is the HVAC planner, not the architect. Sounds odd for a solid fuel stove chimney, but it belongs to the technical system. Alternatively, the stove manufacturer or seller should also provide technical minimum specifications.
2) How the draft should look is clarified by the Bezirksschornsteinfeger. He is responsible for the structural approval.