Fireplace Design – A real burning issue.
Mantlepiece and grate styles have altered but the basic structural elements of a fireplace have not radically changed for hundreds of years. The early combination of a large stone or brick opening with a chimney built over it evolved from the obvious fact that smoke rises, rather than from a scientific understanding of how a well-designed flue system works. Consequently early wood and later coal-burning fires were very inefficient and it was not until a certain Benjamin Thompson (also known as Count Rumford) produced his thesis on the principles of fireplace design in 1799 that smaller grates and improvements in the internal shape of the openings were introduced.
A brick or stone enclosure forms the basis of the fireplace. Variously known as the fireplace opening or recess or builders opening, it may be set flush with the wall or built out into the room, forming a chimney breast. This chimney breast rises through the height of the house, emerging through the roof to form a chimney stack. At the top of the opening the gather and flue combine to carry the smoke up the chimney. If the chimney is shared by several fireplaces on different floors, it may contain more than one flue.
The masonry over the fireplace opening is supported by a lintel or a brick arch. Old inglenook fireplaces used massive oak beams, whereas a strong iron strap usually supports an early brick arch. Later fireplaces may have a straight arch supported by angle iron, and by the twentieth century cast concrete lintels were the norm.
A hearth, constructed from non-combustible materials such as stone or tile-faced concrete, projects out into the room to protect the floor from falling ashes. In most old houses the hearth was set flush with the floor, although sometimes a superimposed one was used to raise the level. The space within the fireplace opening, known as the back hearth, is usually level with the hearth itself. A dog grate for burning wood or coal can be placed on this back hearth. However, by the mid-nineteenth century the mass produced cast-iron register grate which filled the opening, had become the fashion.
To complete the assembly, a mantelpiece or mantel ? or fireplace surround, as it is often called today ? is fitted to frame the grate or fireplace opening. The mantel may be constructed from stone, slate, marble, wood or cast iron. The walls around it may be finished with wood paneling, or more commonly with plaster, and in some cases the mantel extends upwards to form an impressive chimneypiece. Mirrored overmantels were introduced in the late eighteenth century, and these became the classic feature of Victorian sitting rooms.
Within this fireplace an open fire burning wood or coal is a cheerful sight, but if it is your only source of heat, as it was for centuries, this romantic image can soon fade especially if the fire does not burn properly. Getting a fire started and keeping it alight then becomes a challenge, if not a chore. For wood and coal fires to burn well a good supply of air is needed under the grate, as well as a means of escape for the hot gases and smoke. With the fuel safely contained within the fireplace opening on a grate, free circulation of air is possible and waste ash can fall through the grate so the fire is not stifled. If the chimney is inadequate or the flow of air is restricted the fire will not function effectively.