The sides of the fireplace should be vertical up to the throat, or
damper opening (_ff_ fig. 34). The throat should be 6 to 8 inches or
more above the bottom of the lintel and have an area not less than
that of the flue and a length equal to the width of the fireplace opening.
Starting 5 inches above the throat, _ee_, the sides should be drawn in at
_tt_ to equal the flue area.
Proper throat construction is so necessary to a successful fireplace
that the work should be inspected several times a day during construction
to make certain that the side walls are carried up perpendicularly until
the throat is passed and that the full length of opening is provided.