Table 3 gives recommended dimensions for fireplaces of various widths and
heights.
If a damper is installed, the width of the opening j, figure 34, will
depend on the width of the damper frame, the size of which is fixed by
the width and depth of the fireplace and the slope of the back wall. The
width of the throat proper is determined by the opening of the hinged
damper cover. The full damper opening should never be less than the flue
area. Responsible manufacturers of fireplace equipment give valuable
assistance in the selection of a suitable damper for a given fireplace. A
well-designed and well-installed damper should be regarded as essential
in cold climates.
When no damper is used, the throat opening j should be 4 inches for
fireplaces not exceeding 4 feet in height.