Chimney in stead of a fan?

[Peer Bentzen]

I have been wanting to ask this one for a long time: Has anyone tried with a
chimney?
  I remember, in the good ol' days of the MacPlus and before, there was a
company that offered a chimney to mount on top of the Mac.
  The idea was to SILENTLY cool the computer with the airflow coming from
from a tall pipe attached to the cooling-grill on top of the computer. This
should create a stream of ascending (warm) air that would drive the whole
thing.
  It looked silly (it was quite tall), but I'd gladly pay that price for
silence1

/Peer