No chimney!

[Timelord]

You would need to get rid of all internal ceilings to just leave the sloped roof. Also when our ancestors used open fires like this, the roof material was thatch or similar and that was semi permeable to the smoke which seeped through it as well as exiting from the central hole.

Using a system like this seems much more efficient, as you are heating the whole airspace and roof material, rather than a good percentage of heat travelling straight up the chimney. I do think that chimneys are inefficient for space heating. Also, the ancient way keeps the critters and mozzie's at bay, whilst gently smoking everything inside with this excellent insect repellent.