The shape of the fireplace proper should be as indicated in figure 13-A.
The back should pitch forward from a point a little less than half way
from the hearth to the top of the opening, and the sides should be
beveled as indicated. Straight back and sides do not radiate as much heat
into the room.
[Illustration: Fig. 16.--This construction without a throat damper
directs the down draft so that it meets the up draft almost at the
throat, which is more faulty than the construction shown in fig. 15, for
there the lid of the damper deflects the down current.]