A while back, I found out that fireplaces actually consist of four parts.
There is the Fireplace part, where your Sims light fires
The Mantle part, which is the part behind the fireplace that is shaped bigger than the fireplace then thins out
The chimney part, which leads from the mantle part to the exhaust part at the top
The exhaust part, which is where the smoke comes out.
(these are my own names for them.)
Now, if you use Moveobjects on, you can separate each part (and even sell them!), so that you can have a fireplace that takes up little room!
Also, if a sim lights a fire in the fireplace before you do this, and remove every part but the exhaust, you can have a free "fog" effect. This is especially useful for those without Ambitions, and therefore the fog emitter.
Hope this proves useful for you homebuilders!