The campfire works 2m (length) x 2m (width) x 2m (height), 4 times in each direction. Or simplier 4 floor tiles around the campfire. Up & down too.

you can place a fire on core wood

While certainly not helpful early game, you can put fires on top of iron wood beams. I just make a little criss cross in one square and plop one down on any floor I like.

Also, when you get to the point where you can build with stone, you can put a piece of stone flooring on the second floor and place the fire on that.

Yes, it’s a dome hit box. You can tell when building walls all of a sudden u are above the ‘dome’ as you say and can’t build anymore. Good question! Skal!

The height of the fire reaches pretty high, I'd try putting one on the first floor. If that doesn't work you could hang a brazier up by your bed.

You can raise ground to where you need your fire to sit and carve away anything you don't need. You can place the fire outside of your main structure (just outside) then build a wooden chimney using the wall pieces. Use the longer pieces of reg wood vertical as a stand-off and put a 45 degree apex roof piece over the hole. you can build it around one wooden floor tile or two, if you place the "seems" of the walls facing out.

When doing a chimney you need at least 1 floor tile of unobstructed flow above the fire for vent.

Or if you make ceiling high enough you wont need to vent smoke and you can place the fire in the center (again raise ground to wherever you need fire to be)

thank for the info! i was able to place one on the ground floor with a chimney and it works great!