Here is the flue on our fire, fire is located in downstairs living room, the flue passes thru floor area up in to the bedroom up above and thru the raked 40deg pitch roof to outside, the number of flue skins increase as it rises. Double skin from fire to underside of downstairs ceiling, as it passes thru the floor joist it jumps to triple skin with a drop box around it so like fourth skin. The joist area is lined with a fire rated fibro product. The triple skin then continues up thru bedroom before exiting thru roof ceiling, here it is triple skin with drop box again. The flue upstairs gets luke warm to touch with a hot fire, but the room can get hot. I installed this 23 years ago and has worked well. When installing flues/fire places the length of flue can impact on the fires ability to draw.
My wife would say "excuse the mess in the picture"
