Design the route before the roof
Sketch the fireplace, the space above it, and the opening to the outside before you finish the room. A chimney needs a clear route; an impressive silhouette is not the whole job.
Keep the layout simple for your first test. Light the fire, observe where the smoke collects, then adjust the opening and roof clearance in small steps.
Test the room you will actually use
Check the spaces around the bed, workbench, and stairs. A room that looks clear at the doorway may behave differently where your Viking spends time.
Retest after changing floors, ceilings, or the chimney cap. The goal is a usable room, not simply a nice screenshot.
The show’s inspection note
Bjorn calls it an indoor fireplace. The inspection calls it a smoke storage facility. Make the first test before installing the trophy wall.
This is a planning checklist for in-game builds. Test your particular design in your current game version, especially when using mods.