"mm" wrote in message
...
How do I accurately figure out where air is blowing out from, from my
furnace flue area, which is next to my hot air duct.

I'v used a match, but it keeps blowing out. Tonight I took a pencil
and thumbtacked a thin strip of cellophane-like stuff to the end of
it. Later I added a narrow strip of thin cloth. They blow like
crazy when the pencil is on the right side of the flue, but I can't
seem to narrow down where the origin is.

You can buy a smoke pen or light one of those incense things that smoke.
They will generate smoke, but by smoldering, no open flame to blow out.