- mm wrote:

It was a story question and started off by saying that a tall chimney
drew better.

Norman asked Why.

I've got my guess, but I don't know for sure either.

Insufficient chimney height
(from http://www.chimneysweeponline.com/hodraft.htm)

Chimneys usually draw at least a small amount of air, even when there is no
fire below: this phenomenon is called ambient updraft. Ambient chimney
draft occurs because the top of the flue extends upward several feet, into
a lower density atmosphere than exists at the bottom. Thus, air is drawn up
the chimney in much the same way as liquid is drawn up a soda straw when
you reduce the air density inside your mouth.

Most wood stove manufacturers require a minimum stack height (stovepipe and
chimney) of at least 16 feet. Code requires that all woodstove and wood
fireplace chimneys must extend at least two feet above any part of the roof
within ten feet. Given that topographical and atmospheric conditions can
vary considerably from house to house, it is possible for a chimney to
comply with these minimum specifications but still fail to extend upward
into air of low-enough density to establish ambient updraft. It is not
uncommon for fireplaces and stoves in houses that are surrounded by hills
or trees, for example, or that are located in the high-density air that
often surrounds large bodies of water, to need more chimney height than the
minimum required by code.