In building a successful contemporary fireplace, there are at least six things that must receive attention. They are the flue or chimney, smoke chamber, throat, firebox, hearth, and mantel. Of the six, the least important, from the standpoint of construction, are the outer hearth and mantel. To be sure, they are the parts that give the fireplace a decorative effect; but they are not essential to the operating efficiency of the installation.
After the selection of the design for the mantel, the next important step is to determine the size. Too small an opening restricts the amount of heat thrown into the room. The average fireplace is from 30 to 40 inches in width between the jambs. The height of the fireplace and the depth of the fireplace from front to back do not vary to the same extent as the width of the fireplace. The table on page 71 will show you the proper proportions.
The shape of the firebox is important. Its sides should be splayed, that is, drawn in toward the back at an angle of about 15 degrees with the front, or about three inches for every foot. The back of the fireplace should be vertical for a distance of approximately ten inches; then drawn forward to a point where the damper rests upon the masonry. This arrangement provides for throwing more heat into the room.
The ash dump should be placed directly below the fire or the inner hearth so the ashes may be worked through it to the ashpit below. A door to the ashpit at the level of the basement floor will make it easy to remove the ashes.
The throat of a contemporary fireplace is that portion between the top of the firebox and the smoke chamber. It should always be as wide as the fireplace is wide and from four to five inches in depth. By the use of a Majestic Fireplace Damper and Throat combined, this detail of construction is automatically and satisfactorily taken care of, for each damper is properly and scientifically designed to meet the required conditions.
The back edge of the damper should always rest on the forward edge of the smoke shelf. The joint between the damper and the bottom of the smoke shelf should be tightly sealed with mortar so that it is impossible for flames to get to the flue, except through the damper throat.
The smoke chamber is that portion of the fireplace immediately above the throat or damper. A great deal of care should be used to see that pro[x*r dimensions are maintained, that the front of the wall is not drawn in so abruptly as to interfere with the rising smoke, and that all surfaces are smooth and free from large projections.
The bottom of the smoke chamber is called the smoke shelf that is, the portion of the smoke chamber between the damper or throat and the back wall of the smoke chamber. It is absolutely essential to provide a smoke shelf, because in every flue there is what is known as a back draft. Back draft is caused because the front wall of the flue is warmer than the back wall when the fire is burning, and the gases Missing upward along the front wall create a suction down the back wall, resulting in a down draft of outside air. When this down draft meets the smoke shelf, it is deflected by the damper valve plate and carried up again with the rising gases from the fire.
The smoke shelf should be the full width of the throat, never less than eight inches deep, and it may vary from this dimension to 12 inches or more, depending upon the depth of the fireplace itself. See illustration.
The flue is, of course, a very important factor. Its cross section should be at least one-tenth of the area of the front opening of the fireplace. A flue having an area greater than one-tenth of the area of the finished opening is not objectionable, but one having less dooms the fireplace to unsuccessful operation.
The flue should be lined with a fireclay flue lining properly bonded together and to the masonry of the chimney. The area of the flue should be maintained for the entire height of the chimney and not contracted at the top. All turns and bends should be as gradual as possible, with no angle more than 30 degrees from the vertical. And every fireplace should have its own flue. Never connect any other heating apparatus to a fireplace flue.
The chimney should project at least three feet above any flat roof and two feet above the ridge of a hiproof.
In the table below are shown all the essential dimensions needed in the construction of a successful contemporary fireplace. The dimensions are worked out on a basis of the width of the fireplace opening. Slight variations in this dimension will alter the other dimensions somewhat, but the proportions may be easily worked out.
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