[Illustration: Perspective view of the fireplace, showing the shape of the various parts as built without a cast-iron throat damper]
There are other types of dampers, most of them patented and all of them aiming to provide an adjustable opening in the throat in some way. One or two of these have a knob or handle projecting through the brickwork of the arch, permitting the convenient adjustment of the damper from outside. As a general principle, however, it is well to choose the simplest possible device that will secure the desired result.
The terra cotta flue lining which is shown in the sectional diagram is not absolutely necessary, of course, as it is a rather modern introduction and unnumbered fireplaces have served their purpose without it. There is no question, however, regarding its worth, for it provides a flue with smooth, regular sides that will not clog nearly so readily as an ordinary brick flue. Besides that, it has the advantage of permitting a thinner wall for the chimney. It is dangerous to build a chimney with a single four-inch thickness of brick between the flue and whatever may adjoin the chimney. Of course no wood should be allowed to come within an inch or two of the brickwork in any event, but with a single thickness of brick, unlined, there is always the danger that the mortar will crumble from a joint and leave an opening through which it would be an easy matter for sparks or flame to do considerable damage. The introduction of a flue lining, however, into the chimney built in this way makes it entirely safe, provided the joints between sections of flue lining are carefully filled and made smooth with cement mortar.
The sectional diagram, it will be noticed, indicates a difference between the main back wall of the chimney, eight inches thick, and the brickwork laid inside the fire chamber to form the hearth and the back. The reason for this separation is that the rough brickwork of the chimney is always laid first as simply as possible, leaving the fire chamber with its sloping back and sides and the hearth to be filled in later with a better grade of brick or perhaps another kind. Frequently, also, tile will be combined with the brick finish as a hearth or facing.