You likely do not have any problem at all, and are needlessly worried.
Unless you are pretty sure you can feel a draft down to the basement or
attic, then you probably don't.
On an interior wall, the floor should do a good job keeping your
conditioned interior air from going down to the basement. The floor
most likely continues right under the interior walls. Same goes for the
ceiling (the 2x4 cap on the wall framing would keep most air from
getting up to the attic (or the floor above). And the wall studs would
keep air from moving horizontally for any distance beyond the end of
the door pocket.
If you are still worried though, convince yourself using your smoke
trick. Maybe one or two of your doors has a specific problem (an old
plumbing hole drilled in the floor that could be plugged, etc.), but
most will probably be fine as they are.
A baloon frame, isn't conventional. Or, well, it is not these days,
A "conventional" frame house is built one floor at a time, sort of. It
goes like this: First a floor is built. then 2x4s are nailed flat
horizontally on the floor where the walls will be. Then 2x4s (about 8
ft tall) are nailed vertically, and another 2x4 nailed horizontally
across the tops of all them. Then a floor is built on top of this. Then
build walls for the next floor, and another floor on top of that, and
so on. (Builders do it in a slightly different order, but to the same
In a baloon frame house, the exterior walls are built straight up two
or three stories high, using 2x4s that are 20ft tall or more. Then the
upper floors are sort of suspended in between these walls.
The difference is, with no insulation (and no "blocking" either), a
balloon frame house will have a continuous wall cavity the entire
height of the house, maybe even connecting the basement directly to the
attic. In a conventional house, each cavity is interrupted by the
floors and horizontal 2x4s at each floor. Hence, no possible air
connection from one floor to the next.