Stubby wrote:
My house has a short (15') interior wall between two bathrooms. The ends
are up against two closets. All the pipes and septic stack are in the
wall. The bottom rests on a concrete slab and the top is up against the
ceiling. The attic is filled with about 8" of pink bats for insulation.

Recently, I had to open a 8" hole in the closet on one end of the wall
just above the floor. There was a fairly strong cool draft coming out
of the hole. My guess was that the draft was outside air temperature,
but I can't figure how outside air was getting in.

The draft must be coming down from the attic. There are a few places
where electric cables go through into the wall. However, I can't
believe there is enough space around them to admit the amount of air I
was feeling.

You don't wan't to say why you are cutting a hole in a closet wall. It
is outside air from the attic. It is common for there to be a draft
above a partition wall. They are sometimes framed in a way that
creates a kind of chimmey effect. Even a gap between studs can cause
the effect. Many installers make no special effort to prevent a draft
in that area. If you go up in the attic and uncover the bats in that
area above the partition you will see what I mean.