The fireplace has been called the central feature of the home and as such should be given careful consideration by the architect.
The form, proportions and material must be such that the fuel for which the fireplace is designed will burn in it readily without sending gas or smoke out into the room.
Heat is thrown out by radiation, reflection and by movement of the heated air. If the side walls of the fireplace slope in as they extend back, they will reflect heat out into the room, which would not be the case if they ran straight back. Sloping the back wall as shown on Plate 61 also helps to reflect the heat out into the room.
Any chance down-draft in the chimney will be arrested by the smoke shelf as shown by the arrows in the section, thus preventing the smoke from being driven into the room.
The amount of opening in the throat must vary with different conditions of the fire and atmosphere, but when wide open, must be equal in area to the flue above. To allow for adjusting the size of the throat, a damper should be built into it. This is nothing more than a large simple valve for controlling the size of the throat.
All dimensions of the fireplace depend on the size of the opening into the room. At the top of Plate 61 is a diagram of a fireplace properly proportioned and a list of dimensions for several sizes of openings.
When an iron grate or basket is to be used for burning coal, the dimensions and shape of the basket will determine to a certain extent the size and proportions of the fireplace.
All fireplaces, except those for gas, should be lined with 4 inches of fire brick.
If wood is to be the fuel, the fireplace should be about 18 inches deep.
The floor is protected from the heat of the fire by the hearth which is built of brick, stone, tile, etc. There are several methods of supporting the hearth, two of which are shown on the drawing. The usual method in wooden floors is by means of the trimmer arch as shown in the sectional view. The hearth may be carried on the joist as indicated in the pictorial section but shrinkage of the joist will cause cracks to open up in the hearth which is not the case with the arch shown in the orthographic section.