Computed from Formula (28). For brick or brick-lined stacks, increase
the diameter 6 per cent]
Height and Diameter of Stacks--From this formula (27) it becomes evident
that a stack of certain diameter, if it be increased in height, will
produce the same available draft as one of larger diameter, the
additional height being required to overcome the added frictional loss.
It follows that among the various stacks that would meet the
requirements of a particular case there must be one which can be
constructed more cheaply than the others. It has been determined from
the relation of the cost of stacks to their diameters and heights, in
connection with the formula for available draft, that the minimum cost
stack has a diameter dependent solely upon the horse power of the
boilers it serves, and a height proportional to the available draft
required.
Assuming 120 pounds of flue gas per hour for each boiler horse power,
which provides for ordinary overloads and the use of poor coal, the
method above stated gives: