The dimensions of a flue for adequate draft depend principally on
the grate area and type of heating plant 1 and on the kind of fuel to be
burned, both of which should be determined before construction is
begun. If a chimney is found to be inadequate the only method of
improving it, short of reconstruction, is to increase its height. This is
not always effective and is often impracticable.
Table 1 gives the sizes of fire-clay flue linings ordinarily provided
for boilers, furnaces, stoves, or convection heaters burning soft coal.
These sizes have proved satisfactory for average flat-grate furnaces
under normal conditions. Manufacturers of heating equipment
usually specify certain requirements in chimney construction and will
not guarantee the performance of their heaters unless these requirements
are met. Therefore their recommendations should be followed
when differing materially from the dimensions given in this bulletin.